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  • 1
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    Numerical and Analytical Methods for Scientists and Engineers Using Mathematica (2003)
    Wiley
    In:  Hoboken, NJ, 633 pp., Wiley, vol. 16B, no. 2, pp. 125-169, (ISBN 0-471-26610-8)
    Details
    Publication Date: 2003
    Keywords: Textbook of mathematics ; Data analysis / ~ processing ; Modelling ; software ; manual ; computer ; algebra ; symbolic ; mathematics
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Habitat differentiation vs. isolation-by-distance: the genetic population structure of Elymus athericus in European salt marshes (2003)
    Wiley
    In:  Molecular Ecology, 12 (2). pp. 505-515.
    Details
    Publication Date: 2017-07-18
    Description: We investigated genetic differentiation among populations of the clonal grass Elymus athericus, a common salt-marsh species occurring along the Wadden Sea coast of Europe. While E. athericus traditionally occurs in the high salt marsh, it recently also invaded lower parts of the marsh. In one of the first analyses of the genetic population structure in salt-marsh species, we were interested in population differentiation through isolation-by-distance, and among strongly divergent habitats (low and high marsh) in this wind- and water-dispersed species. High and low marsh habitats were sampled at six sites throughout the Wadden Sea. Based on reciprocal transplantation experiments conducted earlier revealing lower survival of foreign genotypes we predicted reduced gene flow among habitats. Accordingly, an analysis with polymorphic cross-species microsatellite primers revealed significant genetic differentiation between high and low marsh habitats already on a very small scale (〈 100 m), while isolation-by-distance was present only on larger scales (60–443 km). In an analysis of molecular variance we found that 14% of the genetic variance could be explained by the differentiation between habitats, as compared to only 8.9% to geographical (isolation-by-distance) effects among six sites 2.5–443 km distant from each other. This suggests that markedly different selection regimes between these habitats, in particular intraspecific competition and herbivory, result in habitat adaptation and restricted gene flow over distances as small as 80 m. Hence, the genetic population structure of plant species can only be understood when considering geographical and selection-mediated restrictions to gene flow simultaneously.
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  • 3
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    A new green-tide-forming alga, Ulva ohnoi Hiraoka et Shimada sp. nov. (Ulvales, Ulvophyceae) from Japan (2004)
    Wiley
    In:  Phycological Research, 52 (1). pp. 17-29.
    Details
    Publication Date: 2017-11-24
    Description: Ulva ohnoi Hiraoka et Shimada sp. nov. (Ulvales, Ulvophyceae) is described from southern and western Japan and is characterized by the following combination of features: (i) the large, fragile, easily torn thalli, which are 30–55 μm thick in the upper and middle regions and often have microscopic marginal teeth; (ii) the production of zoids in the upper marginal region; (iii) a regular alternation of dioecious gametophytes and a sporophyte; (iv) the production of free-floating thalli from torn-off attached thalli, which reproduce vegetatively by fragmentation and form green tides in summer to autumn; (v) disorderly arranged cells that are polygonal or quadrangular in the upper and middle regions; and (vi) the chloroplast covering the outer face of cell, with 1–3 pyrenoids. Ulva ohnoi differs from U. armohcana Dion et al., U. fasciata Delile, U. reticulata Forsskal, U. scandinavica Eliding and U. spiulosaOkamura et Segawa, which all possess microscopic marginal serrations, in thallus shape, cell shape or life history pattern. It is also distinguished from morphologically similar species by sequences of the nuclear encoded internal transcribed spacers and the 5.8S ribosomal RNA gene and the plastid encoded large subunit of ribulose-l,5-bisphosphate carboxylase/oxgenase gene. Furthermore, crossing tests demonstrate that there is a reproductive boundary between U. ohnoi and the most closely related species, U. fasciata and U. reticulata.
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  • 4
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    Do commonly used indices of β-diversity measure species turnover? (2001)
    Wiley
    In:  Journal of Vegetation Science, 12 (4). pp. 545-552.
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    Publication Date: 2017-09-15
    Description: Indices of β-diversity are of two major types, (1) those that measure among-plot variability in species composition independently of the position of individual plots on spatial or environmental gradients, and (2) those that measure the extent of change in species composition along predefined gradients, i.e. species turnover. Failure to recognize this distinction can lead to the inappropriate use of some β-diversity indices to measure species turnover. Several commonly-used indices of β-diversity are based on Whittaker's βW (βW = γ/α, where γ is the number of species in an entire study area and α is the number of species per plot within the study area). It is demonstrated that these indices do not take into account the distribution of species on spatial or environmental gradients, and should therefore not be used to measure species turnover. The terms ‘β-diversity’ and ‘species turnover’ should not be used interchangeably. Species turnover can be measured using matrices of compositional similarity and physical or environmental distances among pairs of study plots. The use of indices of β-diversity and similarity-distance curves is demonstrated using simulated data sets.
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  • 5
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    Regulation of gas vesicle content and buoyancy in light- or phosphate-limited cultures of Aphanizomenon flos-aquae (Cyanophyta) (2004)
    Wiley
    In:  Journal of Phycology, 23 (1). pp. 70-78.
    Details
    Publication Date: 2018-07-20
    Description: Measurements of the gas vesicle space in steady‐state light or phosphate‐limited cultures of Aphanizomenon flos‐aquae Ralfs, strain 7905 showed that gas vesicle content decreased as energy‐limited growth rate increased hut was the same at several phosphate‐limited growth rates. Upon a decrease in growth irradiance, gas vesicle content did increase in phosphate‐limited cultures, hut the cultures remained nonbuoyant as long as P was limiting. Buoyant, energy‐limited cultures lost their buoyancy in less than 2 h when exposed to higher irradiances. The primary mechanism for buoyancy loss was the accumulation of polysaccharide as ballast. Collapse of gas vesicles by turgor pressure played a minor role in the loss of buoyancy. When cultures were exposed to higher irradiances, cells continued to synthesize gas vesicles at the same rate as before the shift for at least 1 generation time. The amount of ballast required to make individual filaments in the population sink varied 4‐fold. This variation appears to be due to differences in gas vesicle content among individual filaments.
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  • 6
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    Taxonomy and Ecology of Sponge-AssociateMarionina spp. (Clitellata : Enchytraeidae) from the Horomatangi Geothermal System of Lake Taupo, New Zealand (2004)
    Wiley
    In:  International Review of Hydrobiology, 89 (1). pp. 58-67.
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    Publication Date: 2017-06-28
    Description: The dissection of Heterorotula sponges collected in an area of geothermal activity at 126–145 m depth on the floor of Lake Taupo (de Rondeet al., 2002) revealed a dense population of associated Enchytraeidae. They represent three species of Marionina, two of which known but exotic (the Palaearctic M. ripariaBretscher, 1899 and the Chinese M. seminudaXie and Rota, 2001), and one new to science, M. spongicola sp. n. This is the first report of an ecological association between enchytraeids and poriferans in the lake profundal zone. The possible nature of such relationship (casual contact for feeding or dwelling for food and shelter) is discussed.
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  • 7
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    The use of Fick's First Law for predicting porewater nutrient fluxes under diffusive conditions (2001)
    Wiley
    In:  Hydrological Processes, 15 (13). pp. 2435-2451.
    Details
    Publication Date: 2020-07-29
    Description: Porewater fluxes into or out of the sediments in aquatic systems are frequently estimated using Fick's First Law. This assumes that diffusive processes control the transport of nutrients. As a corollary, advection, bioturbation and chemical processes are assumed not to be significant. Through a series of sediment core incubations, this paper seeks to quantify the uncertainties involved in such assumptions. Duplicate sediment cores were collected from 28 sites along the Swan–Canning Estuary, returned to the laboratory and incubated under oxic or anoxic conditions. Porewater nutrient concentrations, sediment porosity and initial nutrient concentrations in the overlying water were measured. These parameters were used to estimate the expected nutrient fluxes via Fick's First Law. The estimated fluxes were then compared with measured fluxes of nutrients out of the sediments over the incubation period. Severe bioturbation occurred in several of the anoxic treatments, resulting in large releases of nutrients into the overlying water. Aside from these bioturbated cores, phosphate and ammonium fluxes under anoxic conditions are well predicted by Fick's First Law. Nitrate fluxes are predicted well under oxic conditions. For coarse sediments (D10 averaging 0·3 mm) and under redox conditions favourable for nutrient release, Fick's First Law predicted close to 100% of the observed fluxes. For finer grain sediments (D10 〈 0·01 mm), Fick's First Law overestimated the observed flux by up to 40%. Under unfavourable oxygen conditions, chemical retardation processes are likely to dominate fluxes, and the error associated with using Fick's First Law is increased. These results confirm the usefulness of using Fick's First Law for a baseline estimate of nutrient fluxes under favourable redox conditions. Much greater care must be taken when using Fick's First Law to estimate nutrient fluxes under unfavourable redox conditions, or under conditions when bioturbation is likely to be severe.
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  • 8
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    Effects of attached data loggers on the activity budgets of captive Humboldt Penguins (2002)
    Wiley
    In:  Zoo Biology, 21 (4). pp. 365-373.
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    Publication Date: 2017-12-05
    Description: Although they can provide valuable information on at-sea ecology, data-loggers may adversely affect energetics, diving performance, and breeding success of equipped birds. With the aim of determining the effects of leg-attached data-loggers on the activity budgets of Humboldt penguins (Spheniscus humboldti) while on land, we equipped birds kept at the Landau Zoo, Landau, Germany, with such devices. We followed them during sample periods and recorded the occurrence and length of behaviors. Birds quickly habituated to the devices within 1 day of deployment, and mean rates of device-pecking were low (0.7–1.7 pecks/hr), with device-induced behaviors accounting for 〈1% of the mean daily activity budget. The method of device attachment appears behaviorally less stressful than the traditional tape-based system in which devices are normally attached to the penguin's back. By facilitating the testing of newly developed data-loggers on captive birds, or the development of methods for device attachment, zoos and aquaria may strengthen their role in animal conservation by helping research on free-ranging animals.
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  • 9
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    Stage-specific mortality of Baltic cod (Gadus morhua L.) eggs (2000)
    Wiley
    In:  Journal of Applied Ichthyology, 16 . pp. 266-272.
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    Publication Date: 2017-06-23
    Description: A study on cod egg mortality was carried out in the Bornholm Basin (southern central Baltic Sea) toward the end of July 1996. An initial egg aggregation marked by a satellite-tracked drifter buoy was sampled repeatedly over an 11-day period; profiles of temperature, salinity and dissolved oxygen were concurrently recorded. Three replicate estimates of mortality were obtained for each pair of subsequent developmental stages from newly spawned eggs to early larvae. A consistent pattern of stage-specific mortality coincided well with previous experimental observations. Average daily mortality rates were 7.2% (eggs IA/IB), 38.7% (eggs (IB/II), 25.6% (eggs II/III), 40.0% (eggs III/IV), and 42.3% (eggs IV/early larvae). The cumulative mortality until hatch amounted to 99.9%. Results from hydrodynamic modelling, however, indicated that the drifter's trajectory was influenced by wind stress. Hence, the mortality rates might be biased despite the short sampling intervals; a modification of the sampling design is recommended for future studies.
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  • 10
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    Consumer effects decline with prey diversity (2004)
    Wiley
    In:  Ecology Letters, 7 . pp. 192-201.
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    Publication Date: 2017-02-22
    Description: While consumer species diversity is known to influence the capture of limited resources, little is known about how prey diversity impacts the transfer of energy and matter among trophic levels. Here, we perform a meta-analysis of experiments that have examined the impact of grazers on the biomass of periphytic algae to test the hypothesis that the magnitude of consumer (grazer) effects on prey (algae) depends on the species diversity of the prey assemblage. The analysis reveals that consumer effects tend to decrease as the diversity of a prey assemblage increases. This trend is robust for several different, yet complementary indices of grazer effect size and algal diversity. The trend also remains significant after statistically controlling for a variety of factors that can covary with prey diversity among studies. We discuss several possible mechanisms for the documented pattern, such as diversity enhancing the probability of inedibility and of positive interactions.
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  • 11
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    Cascading predation effects of Daphnia and copepods on microbial food web components (2003)
    Wiley
    In:  Freshwater Biology, 48 (12). pp. 2174-2193.
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    Publication Date: 2017-01-16
    Description: 1. We performed a mesocosm experiment to investigate the structuring and cascading effects of two predominant crustacean mesozooplankton groups on microbial food web components. The natural summer plankton community of a mesotrophic lake was exposed to density gradients of Daphnia and copepods. Regression analysis was used to reveal top-down impacts of mesozooplankton on protists and bacteria after days 9 and 15. 2. Selective grazing by copepods caused a clear trophic cascade via ciliates to nanoplankton. Medium-sized (20-40 mum) ciliates (mainly Oligotrichida) were particularly negatively affected by copepods whereas nanociliates (mainly Prostomatida) became more abundant. Phototrophic and heterotrophic nanoflagellates increased significantly with increasing copepod biomass, which we interpret as an indirect response to reduced grazing pressure from the medium-sized ciliates. 3. In Daphnia-treatments, ciliates of all size classes as well as nanoflagellates were reduced directly but the overall predation effect became most strongly visible after 15 days at higher Daphnia biomass. 4. The response of bacterioplankton involved only modest changes in bacterial biomass and cell-size distribution along the zooplankton gradients. Increasing zooplankton biomass resulted either in a reduction (with Daphnia) or in an increase (with copepods) of bacterial biovolume, activity and production. Patterns of bacterial diversity, as measured by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), showed no distinct grouping after 9 days, whereas a clear treatment-coupled similarity clustering occurred after 15 days. 5. The experiment demonstrated that zooplankton-mediated predatory interactions cascade down to the bacterial level, but also revealed that changes occurred rather slowly in this summer plankton community and were most pronounced with respect to bacterial activity and composition.
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  • 12
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    Structure-activity relationships of oligoagar elicitors towards Gracilaria conferta (Rhodophyta) (2001)
    Wiley
    In:  Journal of Phycology, 37 (3). pp. 418-426.
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    Publication Date: 2018-04-26
    Description: Agar oligosaccharides in the neoagarobiose series were prepared by partial enzyme hydrolysis, separated on Biogel P2 and P4, and analyzed by high-performance anion exchange chromatography with pulsed amperometric detection, yielding neoagarosaccharide fractions with a disaccharide repetition degree ranging from 1 (neoagarobiose) to more than 8 (neoagarohexadecaose). These fractions were analyzed for their biological activity toward the marine red alga Gracilaria conferta (Schousboe ex Montagne) J. et G. Feldmann in terms of increase of oxygen consumption, release of hydrogen peroxide, elimination of epiphytic bacteria, and induction of thallus tip bleaching. The structure–activity and dose–response relationships of neoagarosaccharides were very similar in the respiratory and oxidative burst responses and in their bactericidal properties, with neoagarosaccharides consisting of 6 to 8 disaccharide repeating units being the most active. All these responses were competitively inhibited by the reduced form of neoagarohexaose, neoagarohexaitol. In contrast, the tip-bleaching response was light dependent, required much higher concentrations of neoagarosaccharides, and was not inhibited by neoagarohexaitol, suggesting that it is an unspecific oxidative stress reaction. Putative structural effects on the recognition of endogenous agar-oligosaccharide elicitors by G. conferta are discussed.
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  • 13
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    What happens to the kype of male Atlantic salmon (Salmo salar) that survive spawning? (2004)
    Wiley
    In:  Journal of Morphology, 260 .
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    Publication Date: 2018-04-03
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  • 14
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    Foraging interactions of wandering albatrosses Diomedea exulans breeding on Marion Island with longline fisheries in the southern Indian Ocean: Seasonal and gender effects (2002)
    Wiley
    In:  Ibis, 144 (3). E141-E154.
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    Publication Date: 2017-01-30
    Description: Wandering Albatrosses Diomedea exulans are frequently killed when they attempt to scavenge baited hooks deployed by long-line fishing vessels. We studied the foraging ecology of Wandering Albatrosses breeding on Marion Island in order to assess the scale of interactions with known long-line fishing fleets. During incubation and late chick-rearing, birds foraged further away from the island, in warmer waters, and showed high spatial overlap with areas of intense tuna Thunnus spp. long-line fishing. During early chick-rearing, birds made shorter foraging trips and showed higher spatial overlap with the local Patagonian Toothfish Dissostichus eleginoides long-line fishery. Tracks of birds returning with offal from the Toothfish fishery showed a strong association with positions at which Toothfish long-lines were set and most diet samples taken during this stage contained fishery-related items. Independent of these seasonal differences, females foraged further from the islands and in warmer waters than males. Consequently, female distribution overlapped more with tuna long-line fisheries, whereas males interacted more with the Toothfish long-line fishery. These factors could lead to differences in the survival probabilities of males and females. Non-breeding birds foraged in warmer waters and showed the highest spatial overlap with tuna long-line fishing areas. The foraging distribution of Marion Island birds showed most spatial overlap with birds from the neighbouring Crozet Islands during the late chick-rearing and non-breeding periods. These areas of foraging overlap also coincided with areas of intense tuna long-line fishing south of Africa. As the population trends of Wandering Albatrosses at these two localities are very similar, it is possible that incidental mortality during the periods when these two populations show the highest spatial overlap could be driving these trends.
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  • 15
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    Meta-analysis of cod-shrimp interactions reveals top-down control in oceanic food webs (2003)
    Wiley
    In:  Ecology, 84 (1). pp. 162-173.
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    Publication Date: 2017-02-21
    Description: Here we present a meta-analytic approach to analyzing population interactions across the North Atlantic Ocean. We assembled all available biomass time series for a well-documented predator–prey couple, Atlantic cod (Gadus morhua) and northern shrimp (Pandalus borealis), to test whether the temporal dynamics of these populations are consistent with the “top-down” or the “bottom-up” hypothesis. Eight out of nine regions showed inverse correlations of cod and shrimp biomass supporting the “top-down” view. Exceptions occurred only close to the southern range limits of both species. Random-effects meta-analysis showed that shrimp biomass was strongly negatively related to cod biomass, but not to ocean temperature in the North Atlantic Ocean. In contrast, cod biomass was positively related to ocean temperature. The strength of the cod–shrimp relationship, however, declined with increasing mean temperature. These results show that changes in predator populations can have strong effects on prey populations in oceanic food webs, and that the strength of these interactions may be sensitive to changes in mean ocean temperature. This means that the effects of overfishing in the ocean cascade down to lower trophic levels, as has been shown previously for lakes and coastal seas. In order to further investigate these processes, we establish a methodological framework to analyze species interactions from time series data.
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  • 16
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    Reconstruction of ice complex remnants on the eastern Siberian arctic shelf (2003)
    Wiley
    In:  Permafrost and Periglacial Processes, 14 (2). pp. 187-198.
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    Publication Date: 2015-01-29
    Description: Based on the analysis of seafloor topography together with historical, geological and palaeogeographical data obtained from published and archived sources, the position of former Ice Complex (IC) islands has been reconstructed. Within the Laptev Sea shelf and in the western part of the East Siberian Sea shelf, most of these islands have been destroyed by coastal thermal erosion and thermal abrasion during the last thousand years or so. The IC islands were the remnants of the ice-rich syncryogenic freshwater terrestrial deposits (so called IC), which covered most of the arctic coastal plains and the emerged arctic shelf during the Late Pleistocene. At the present time, sandbanks exist at the places of former IC islands. These sandbanks are the subject of intense seafloor thermal abrasion. The approximate rates of seafloor thermal abrasion and the time of complete disappearance of these islands during the last thousand years have been estimated. The rate is different for different islands and for different time intervals. The most common values are between 0.02 and 0.3 m/year. Schematic maps of the former IC islands within the Laptev Sea and western part of the East Siberian Sea shelves have been compiled.
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  • 17
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    Big Effects from Small Changes: Possible Ways to Explore Nature's Chemical Diversity (2002)
    Wiley
    In:  ChemBioChem, 3 (7). pp. 619-627.
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    Publication Date: 2016-02-19
    Description: Fungi or bacteria that produce secondary metabolites often have the potential to bring up various compounds from a single strain. The molecular basis for this well-known observation was confirmed in the last few years by several sequencing projects of different microorganisms. Besides well-known examples about induction of a selected biosynthesis (for example, by high- or low-phosphate cultivation media), no overview about the potential in this field for finding natural products was given. We have investigated the systematic alteration of easily accessible cultivation parameters (for example, media composition, aeration, culture vessel, addition of enzyme inhibitors) in order to increase the number of secondary metabolites available from one microbial source. We termed this way of revealing nature's chemical diversity the 'OSMAC (One Strain-Many Compounds) approach' and by using it we were able to isolate up to 20 different metabolites in yields up to 2.6 g L(-1) from a single organism. These compounds cover nearly all major natural product families, and in some cases the high production titer opens new possibilities for semisynthetic methods to enhance even more the chemical diversity of selected compounds. The OSMAC approach offers a good alternative to industrial high-throughput screening that focuses on the active principle in a distinct bioassay. In consequence, the detection of additional compounds that might be of interest as lead structures in further bioassays is impossible and clearly demonstrates the deficiency of the industrial procedure. Furthermore, our approach seems to be a useful tool to detect those metabolites that are postulated to be the final products of an amazing number of typical secondary metabolite gene clusters identified in several microorganisms. If one assumes a (more or less) defined reservoir of genetic possibilities for several biosynthetic pathways in one strain that is used for a highly flexible production of secondary metabolites depending on the environment, the OSMAC approach might give more insight into the role of secondary metabolism in the microbial community or during the evolution of life itself.
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  • 18
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    Natural Products from Marine Microorganisms (2002)
    Chemistry Europe | Wiley
    In:  ChemBioChem, 3 (11). pp. 1151-1154.
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    Publication Date: 2020-07-27
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  • 19
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    Temporal variation of the microbial community associated with the mediterranean sponge Aplysina aerophoba (2001)
    Wiley
    In:  FEMS Microbiology Ecology, 38 (2-3). pp. 105-115.
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    Publication Date: 2015-08-27
    Description: Sponges of the Aplysinidae family contain large amounts of bacteria that are embedded within the sponge tissue matrix. In order to determine the stability and specificity of the Aplysina–microbe association, sponges were maintained in recirculating seawater aquariums for 11 days. One aquarium was left untreated, a second one contained 0.45 μm filtered seawater (starvation conditions) and the third one contained 0.45 μm filtered seawater plus antibiotics (antibiotics exposure). Changes in the microbial community were monitored using group-specific, 16S rRNA targeted oligonucleotide probes, by denaturing gradient gel electrophoresis and by electron microscopic observations. Furthermore, the changes in the natural product profile were monitored using high-performance liquid chromatography. The measured parameters showed that a large fraction of the sponge-associated microbial community could not be cleared under the given experimental conditions. Based on these cumulative results we postulate that a large fraction of sponge-associated bacteria resides permanently in the Aplysina aerophoba mesohyl pointing to a highly integrated interaction between the host sponge and associated microorganisms.
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  • 20
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    Isolation and phylogenetic analysis of bacteria with antimicrobial activities from the Mediterranean sponges Aplysina aerophoba and Aplysina cavernicola (2001)
    Wiley
    In:  FEMS Microbiology Ecology, 35 (3). pp. 305-312.
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    Publication Date: 2015-08-27
    Description: The aim of this study was to isolate bacteria with antimicrobial activities from the marine sponges Aplysina aerophoba and Aplysina cavernicola. The obtained 27 isolates could be subdivided into eight phylogenetically different clusters based on comparative sequence analysis of their 16S rDNA genes. The sponge isolates were affiliated with the low (Bacillus) and high G+C Gram-positive bacteria (Arthobacter, Micrococcus), as well as the α-Proteobacteria (unknown isolate) and γ-Proteobacteria (Vibrio, Pseudoalteromonas). One novel Bacillus species was identified and two species were closely related to previously uncharacterized strains. Isolates with antimicrobial activity were numerically most abundant in the genera Pseudoalteromonas and the α-Proteobacteria. The sponge isolates show antimicrobial activities against Gram-positive and Gram-negative reference strains but not against the fungus Candida albicans. A general pattern was observed in that Gram-positive bacteria inhibited Gram-positive strains while Gram-negative bacteria inhibited Gram-negative isolates. Antimicrobial activities were also found against clinical isolates, i.e. multi-resistant Staphylococcus aureus and Staphylococcus epidermidis strains isolated from hospital patients. The high recovery of strains with antimicrobial activity suggests that marine sponges represent an ecological niche which harbors a hitherto largely uncharacterized microbial diversity and, concomitantly, a yet untapped metabolic potential.
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  • 21
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    Symbiosis, infection and pathogenicity (2002)
    Wiley
    In:  In: Molecular Infection Biology. , ed. by Hacker, J. and Heesemann, J. Wiley, New York, USA, pp. 53-56. ISBN 978-0-471-17846-0
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    Publication Date: 2015-09-08
    Type: Book chapter , NonPeerReviewed
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  • 22
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    Crustal architecture and deep structure of the Ninetyeast Ridge hotspot trail from active-source ocean bottom seismology (2001)
    Wiley
    In:  Geophysical Journal International, 144 (2). pp. 414-431.
    Details
    Publication Date: 2018-01-31
    Description: A 550-km-long transect across the Ninetyeast Ridge, a major Indian ocean hotspot trail, provided seismic refraction and wide-angle reflection data recorded on 60 ocean bottom instruments. About 24 000 crustal and 15 000 upper mantle arrivals have been picked and used to derive an image of the hotspot track. Two approaches have been chosen: (i) a first-arrival tomographic inversion yielding crustal properties; and (ii) forward modelling of mantle phases revealing the structure at the crust–mantle boundary region and of the uppermost mantle. Away from the volcanic edifice, seismic recordings show the typical phases from oceanic crust, that is, two crustal refraction branches (Pg), a wide-angle reflection from the crust–mantle boundary (PmP) and a wave group turning within the upper mantle (Pn). Approaching the edifice, three additional phases have been detected. We interpret these arrivals as a wide-angle reflection from the base of material trapped under the pre-hotspot crust (Pm2P) and as a wide-angle reflection (PnP) and its associated refraction branch (PN) from a layered upper mantle. The resulting models indicate normal oceanic crust to the west and east of the edifice. Crustal thickness averages 6.5–7 km. Wide-angle reflections from both the pre-hotspot and the post-hotspot crust–mantle boundary suggest that the crust under the ridge has been bent downwards by loading the lithosphere, and hotspot volcanism has underplated the pre-existing crust with material characterized by seismic velocities intermediate between those of mafic lower crustal and ultramafic upper mantle rocks (7.5–7.6 km s−1). In total, the crust is up to ≈ 24 km thick. The ratio between the volume of subcrustal plutonism forming the underplate and extrusive and intrusive volcanism forming the edifice is about 0.7. An important observation is that underplating continued to the east under the Wharton Basin. During the shield-building phase, however, Ninetyeast Ridge was located adjacent to the Broken Ridge and was subsequently pulled apart along a transform fault boundary. Therefore, underplating eastwards of the fracture zone separating the edifice from the Wharton Basin suggests that prolonged crustal growth by subcrustal plutonism occurred over millions of years after the major shield-building stage. This fact, however, requires mantle flow along the fossil hotspot trail. The occurrence of PnP and PN arrivals is probably associated with a layered and anisotropic upper mantle due to the preferential alignment of olivine crystals and may have formed by rising plume material which spread away under the base of the lithosphere.
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  • 23
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    New microsatellite markers for the snow crab Chionoecetes opilio (Brachyura: Majidae) (2003)
    Wiley
    In:  Molecular Ecology Resources, 3 (4). pp. 644-646.
    Details
    Publication Date: 2020-06-30
    Description: Five microsatellite markers were developed for the snow crab (Chionoecetes opilio) and polymerase chain reaction conditions and/or primer sequences of three previously developed microsatellites were adapted for fluorescent labelling analysis. All loci were analysed in 449 individuals from 11 sampling sites in the northwest Atlantic. The high degree of polymorphism exhibited by these microsatellites (mean of 34 alleles per locus and mean observed heterozygosity of 0.76) suggests that they will be suitable for spatial and temporal genetic analysis of C. opilio populations.
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  • 24
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    Crustal underplating and its implications for subsidence and state of isostasy along the Ninetyeast Ridge hotspot trail (2000)
    Wiley
    In:  Geophysical Journal International, 142 (2). pp. 643-649.
    Details
    Publication Date: 2018-01-31
    Description: Recent seismic field work has revealed high lower-crustal velocities under Ninetyeast Ridge, Indian Ocean, indicating the presence of crustal underplating (Grevemeyer et al. 2000). We used results from Ocean Drilling Program (ODP) drill cores and cross-spectral analysis of gravity and bathymetric data to study the impact of the underplating body on the subsidence history and the mode of isostatic compensation along Ninetyeast Ridge. Compared with the adjacent Indian basin, the subsidence of Ninetyeast Ridge is profoundly anomalous. Within the first few millions of years after crustal emplacement the ridge subsided rapidly. Thereafter, however, subsidence slowed down significantly. The most reliable model of isostasy suggests loading of a thin elastic plate on and beneath the seafloor. Isostatic compensation of subsurface loading occurs at a depth of about 25km, which is in reasonably good agreement with seismic constraints. Subsurface loading is inherently associated with buoyant forces acting on the lithosphere. The low subsidence may therefore be the superposition of cooling of the lithosphere and uplift due to buoyant material added at the base of the crust. A model including prolonged crustal growth in the form of subcrustal plutonism may account for all observations.
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  • 25
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    Primary productivity of planet earth: biological determinants and physical constraints in terrestrial and aquatic habitats (2001)
    Wiley
    In:  Global Change Biology, 7 (8). pp. 849-882.
    Details
    Publication Date: 2018-05-16
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  • 26
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    Control of microbenthic communities by grazing and nutrient supply (2002)
    Wiley
    In:  Ecology, 83 (8). pp. 2205-2219.
    Details
    Publication Date: 2017-02-17
    Description: In periphyton communities, autotrophic algae and prokaryotes live in close spatial proximity to heterotrophic components such as bacteria and micro- and meiofauna. In factorial field experiments, we manipulated grazer access and nutrient supply to periphyton communities and measured the effects on algal, ciliate, meiofaunal, and bacterial biomass. We tested whether grazing macrozoobenthos affects all periphytic components (generalist consumption), whether nutrient effects propagate through the community, and whether interactions between the different periphyton groups allow for indirect feedback mechanisms. The experiments were conducted during three different seasons in a meso-eutrophic lake in Sweden (Lake Erken) and at an adjacent coastal marine site (Väddö) of similar productivity, but with contrasting grazer fauna. We found strong direct effects of nutrients and grazing on algae at both sites. Algal biomass increased in fertilized treatments and was significantly reduced when grazers were present. The algae clearly dominated the system quantitatively and were positively correlated to the biomass of ciliates and meiofauna. The effects of grazing and nutrients were more complex for heterotrophs than for algae. Generally, the presence of grazers tended to increase the biomass of bacteria, ciliates, and meiofauna. Thus, macrograzers were not generalist consumers of the entire community, but mainly reduced algae. Furthermore, the results suggested strong indirect effects of grazing, presumably through changes in nutrient supply and algal size structure. Nutrient enrichment had weak and inconsistent effects on bacterial, ciliate, and meiofaunal biomass. There was thus no complete propagation of bottom-up effects through the community, and strong internal feedback mechanisms within the periphyton mediated the effects of macroconsumers and nutrient enrichment.
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  • 27
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    Magellanic Penguins (Spheniscus magellanicus) commuting through San Julian Bay; Do current trends induce tidal tactics? (2001)
    Wiley
    In:  Journal of Avian Biology, 32 (1). pp. 83-89.
    Details
    Publication Date: 2016-04-25
    Description: The behaviour of Magellanic Penguins Spheniscus magellanicus commuting between their foraging areas and breeding areas in San Julian Bay, Argentina was studied to examine whether tidal rip currents affected travelling patterns. Although there was no apparent relationship between departure and arrival patterns and the state of the tidal cycle, birds travelling against the current dived for longer periods and had shorter rests on the surface than birds travelling with the current. In addition, birds swimming against the current hugged the banks of tidal rivers much more closely than did birds swimming with the current, thus reducing the magnitude of the current against which they had to swim. In cases of extremely high current speeds, birds travelling upstream walked. Models regarding the energetics of movement indicate that the strategies adopted by Magellanic Penguins can result in substantial energy savings.
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  • 28
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    Simple methods to obtain preliminary growth estimates for fishes (2003)
    Wiley
    In:  Journal of Applied Ichthyology, 19 (6). pp. 376-379.
    Details
    Publication Date: 2017-07-03
    Description: Explored were methods to derive preliminary information on growth from other known life history parameters such as maximum size and size and age at first maturity. Use was made of the fact that with asymptotic length known, only one point is needed to determine the general shape of a von Bertalanffy growth curve. An empirical relationship was used to predict asymptotic length from maximum observed length. We used mean size reached at age 1 or 2 or mean age and size at first maturity, as is often provided in the literature, to derive preliminary von Bertalanffy growth curves. Results of this approach were then compared with published growth estimates. We used an empirical relationship to predict length at first maturity from asymptotic length when only the age at first maturity was given in the literature. Temperate fishes usually have restricted spawning periods lasting a few months per year and maturity is typically reached in the first, second, third, or later year, i.e. in steps of 12 months, with larger species maturing later. We used data in FishBase (http://www.fishbase.org) to establish typical ranges for age at first maturity and growth performance of temperate fishes as a function of maximum size. We present an approach that uses this framework to derive preliminary growth estimates for species of which only the maximum size is known.
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  • 29
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    Linking the North Atlantic to Central Europe: A high-resolution Holocene tephrochronological record from Northern Germany (2002)
    Wiley
    In:  Journal of Quaternary Science, 17 (1). pp. 3-20.
    Details
    Publication Date: 2017-07-24
    Description: A high-resolution Holocene tephrochronology for northern Germany has been established based on systematic tephrostratigraphical analysis of three peat bogs. Microscopic volcanic ash layers have been traced and characterised petrographically and by the chemical composition of the glass shards. At least 37 ash horizons representing 16 different explosive volcanic eruptions have been identified and many can be correlated between the three sites, up to 100 km apart. The tephra layers can be related to Icelandic volcanic sources and some correlated to the eruptions of Askja 1875, Hekla 3, Hekla Selsund, Hekla 4 and Hekla 5, as well as to unspecified eruptions of Icelandic volcanic systems, e.g. Torfajökull. The source volcanoes for some tephra layers remain unidentified. Some tephra layers were known previously from the North Atlantic region (e.g. Sluggan, Glen Garry), others have not been recorded previously in the literature (e.g. microlite tephra). This study provides the first comprehensive Holocene tephrostratigraphical record for northern Germany, complementing the North Atlantic tephrostratigraphical dating framework, effectively extending it into central Europe. The study shows that Icelandic ash layers are even more widespread than hitherto thought.
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  • 30
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    Small-scale faulting, topographic steps and seismic risk in the Alhambra (Grenada, SE Spain) (2004)
    Wiley
    In:  Journal of Quaternary Science, 19 (3). pp. 219-227.
    Details
    Publication Date: 2017-07-24
    Description: The Alhambra (14th century AD) in Granada (southeast Spain) is built at the summit of a Pliocene to Lower Pleistocene conglomeratic formation. Tens of small-scale normal faults crop out along the northern hillslope of the Alhambra, which have a N130–N150°E strike, dipping 65–75° mostly to the southwest. These are closely spaced faults (approximately 5–30 m) with centimetre to several metre displacements. Several topographic steps in this area coincide with hectometre- to kilometre-scale faults with the same kinematics as the small-scale ones. Some of these faults appear to be active and related to the present seismicity detected in this region, and associated with the cracks and other damage observed in the Alhambra. Several focal mechanisms calculated in this study are in accordance with the dominant NW–SE orientated normal faults. We interpret that the topographic steps of these faults are a consequence of repeated earthquakes during the past 800 ka. The last large earthquake of approximately 5.1 magnitude in this area occurred in 1431, destroying the Alixares Palace, the Arabian fence and part of the Alhambra wall. We consider the seismic risk associated with these faults to be moderate, as the displacement is partitioned into several hectometre- to kilometre-scale faults.
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  • 31
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    Vertical migration by Rhizosolenia spp. (Bacillariophyceae): Implications for Fe Acquisition (2000)
    Wiley
    In:  Journal of Phycology, 36 . pp. 669-674.
    Details
    Publication Date: 2018-04-26
    Description: Available data support a mechanism of buoyancy‐mediated vertical migration by large‐sized diatoms of Rhizosolenia spp. as a means to access “new” nitrogen from deep waters. To assess whether phytoplankton simultaneously satisfy their Fe requirements by this mechanism, field samples collected during summer 1996 at stations located along a transect through the central North Pacific gyre were assayed for the presence of flavodoxin and ferredoxin via Western blot analysis. All samples, regardless of their buoyancy status and the station from which they were collected, had accumulated flavodoxin but not ferredoxin. To understand better the significance of the field results, cultures of Rhizosolenia formosa H. Peragallo were grown in the laboratory with varying levels of total Fe (200 nM–10,000 nM). Fe had little effect on the physiological and photochemical parameters measured for each treatment. Growth rates did not exceed 0.17 d−1 and values of Fv/Fm ranged from 0.48 to 0.62. In addition, R. formosa accumulated only flavodoxin at each level of Fe addition. From these results, it appears that for some rhizosolenids, flavodoxin is constitutively expressed. The underlying basis for the constitutive nature of this flavodoxin is unclear at present, although it is likely that it is ultimately related to chronic Fe deficit incurred in natural waters.
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  • 32
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    Phytoplankton, light, and nutriets in a gradient of mixing depths: field experiments (2002)
    Wiley
    In:  Ecology, 83 (2). pp. 399-411.
    Details
    Publication Date: 2017-02-17
    Description: We studied the effects of water column mixing depth and background turbidity on phytoplankton biomass, light climate, and nutrients in two field enclosure experiments designed to test predictions of a dynamical model. In 1997 and 1998, we created gradients of mixing depth by enclosing the 100-μm-filtered phytoplankton community of a phosphorus-deficient lake in cylindrical plastic bags of varying depth (1.5–15 m) which were continuously mixed. To mimic different levels of background turbidity, we surrounded the transparent enclosure walls with a layer of opaque white (1997) or black (1998) plastic. The experiments were run for 4 wk (1997) and 6 wk (1998). The results supported two key assumptions of the model: specific production and specific sedimentation losses both decreased with increasing mixing depth. At all mixing depths, fast-sinking diatoms dominated the communities. In accordance with model predictions, algal biomass concentration and standing stock (summed over the mixed layer) showed a unimodal relationship to mixing depth when background turbidity was high (1998). When background turbidity was lower (1997), only the ascending limbs of the corresponding relationships were found, which supports the prediction that the mixing depth at which biomass peaks (i.e., becomes predominantly limited by light) increases with decreasing background turbidity. Also in accordance with predictions, light intensity at the bottom of the mixed layer decreased with increasing mixing depth and with increasing background turbidity. Finally, the data supported only the ascending limbs of the predicted inverse unimodal relationships among mixing depth and dissolved inorganic and total water column phosphorus. The absence of descending limbs in these relationships at low mixing depths was probably due to deviations of the experimental systems from two model assumptions. First, the remineralization rate of sedimented phosphorus may have been too slow to equilibrate with sedimentation losses over the experimental periods. Second, biomass yield per unit nutrient (the ratio of seston carbon to phosphorus) was not constant, but decreased with increasing mixing depth. To our knowledge, these are the first field experiments in which the effects of mixing depth on phytoplankton and its resources have been investigated systematically along a large gradient.
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  • 33
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    Evidence for a mid-Pleistocene change of ice-drift pattern in the Nordic seas (2003)
    Wiley | Quaternary Research Association
    In:  Journal of Quaternary Science, 18 . pp. 183-191.
    Details
    Publication Date: 2019-08-08
    Description: Sediment proxy records from a continuous, 1.5 million year long deep-sea sediment core from a site in the western Norwegian Sea were used to obtain new insights into the nature of palaeoceanographic change in the northern North Atlantic (Nordic seas) during the climatic shift of the Mid-Pleistocene Revolution (MPR). Red-green sediment colour and magnetic susceptibility records both reveal significant differences in their mean values when comparing the intervals older than 700 000 yr (700 ka) with those from the past 500 kyr. The timing and duration of these changes indicates that the MPR in the Nordic seas is characterised by a gradual transition lasting about 200 kyr. Together with further sedimentological evidence this suggests that the mid-Pleistocene climate shift was accompanied by a general change in ice-drift pattern. It is further proposed that prior to the onset of the major late Pleistocene glaciations in the Northern Hemisphere a significant proportion of the ice in the eastern Nordic seas originated from a southern provenance, whereas later it dominantly came from the surrounding landmasses.
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  • 34
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    Spatial and temporal variation in biomass and nutrient status of epilithic algae in Lake Erken, Sweden (2002)
    Wiley
    In:  Freshwater Biology, 47 (7). pp. 1191-1216.
    Details
    Publication Date: 2017-01-10
    Description: 1. The aim of this study was to estimate patchiness in biomass and in the internal nutrient status of benthic algae on hard substrata (epilithon) in Lake Erken, Sweden, over different levels of distance, depth and time. Knowledge of the sources and scale of patchiness should enable more precise estimation of epilithic biomass and nutrient status for the entire lake. We focused on the horizontal scale, about which little is known. 2. We sampled epilithon by SCUBA diving and used a hierarchical sampling design with different horizontal scales (cm, dm, 10 m, km) which were nested in two temporal scales (within and between seasons). We also compared two successive years and three sampling depths (0, 1 and 4 m). Biomass was measured as particulate carbon and chlorophyll a (Chl a) and internal nutrient status as carbon : nitrogen : phosphorus (C : N : P) ratios and as specific alkaline phosphatase activity (APA). 3. Horizontal variation accounted for 60–80 and 7–70% of the total variation in biomass and in nutrient status, respectively, at all depths and during both years. Both small and large scales accounted for significant variation. We also found variation with time and depth. Biomass increased in autumn after a summer minimum, and the within-season variation was very high. The lowest biomass was found at 0 m depth. Both N and P limitation occurred, being higher in 1996 than in 1997 and decreased with depth. 4. As a consequence, any sampling design must address variation with distance, depth and time when estimating biomass or nutrient limitation of benthic algae for an entire lake. Based on this analysis, we calculated an optimal sampling design for detecting change in the epilithic biomass of Lake Erken between different sampling days. It is important to repeat the sampling as often as possible, but also the large scales (10 m and km) and the dm scale should be replicated. Using our calculations as an example, and after a pilot study, an optimal sampling design can be computed for various objectives and for any lake. 5. Short-term impact of the wind, light and nutrient limitation, and grazing, might be important in regulating the biomass and nutrient status of epilithic algae in Lake Erken. Patchiness in the nutrient status of algae was not coupled to the patchiness of biomass, indicating that internal nutrients and biomass were regulated by different factors.
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  • 35
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    Problems and suggestions concerning the notation of cadmium stable isotope composition and the use of reference materials (2004)
    International Association of Geoanalysts | Wiley
    In:  Geostandards and Geoanalytical Research, 28 (1). pp. 173-178.
    Details
    Publication Date: 2019-08-08
    Description: Notations for Cd stable isotope compositions and the use of reference materials are discussed. It is proposed that Cd stable isotope data should be reported as variations of the 114Cd/110Cd ratio/ using either the δ114/110Cd or ε114/110Cd notations. Future publications should report results for BAM-1012 Cd, the only currently available international Cd isotope reference material. It is also recommended that “Münster Cd” and a range of specified geological reference materials are used as additional reference materials. The final choice of a primary “zero-delta” reference standard remains the most important outstanding question.
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  • 36
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    Temporal changes in Holocene δ18O records from the northwest and central North Iceland Shelf (2004)
    Wiley
    In:  Journal of Quaternary Science, 19 (4). pp. 321-334.
    Details
    Publication Date: 2020-07-20
    Description: The region of north Iceland is highly sensitive climatically owing to its location with respect to atmospheric and oceanographic fronts. In this study we present total carbonate and δ18O records of benthic and planktic Foraminifera from nine sediment cores from the North Iceland Shelf. The results of this work indicate that the deglaciation of the Vestfirdir Peninsula was completed by 10 200 cal. yr BP. The 8200 cal. yr BP cold event is present only as a minor isotopic event, and seems not to have had much of a cooling effect on the bottom waters of the northwest Iceland shelf. The Holocene maximum warmth, attributed to a stronger North Icelandic Irminger Current, occurred between ca. 7800 and 6200 cal. yr BP. Over the past 4500 cal. yr BP a general cooling trend has occurred on the North Iceland Shelf, and superimposed on this overall cooling trend are a number of oscillations between periods when relatively warmer and cooler waters occupied the shelf. Relatively cooler waters were present at 4200–4000 cal. yr BP, 3200–2900 cal. yr BP, 2500–2350 cal. yr BP and 600–200 cal. yr BP, whereas relatively warmer waters were present on the shelf at 3750–3450 cal. yr BP, 2800–2600 cal. yr BP and 1700–1000 cal. yr BP.
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  • 37
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    Aquaculture production and environmental regulations in Germany (2000)
    Wiley
    In:  Journal of Applied Ichthyology, 16 . pp. 163-166.
    Details
    Publication Date: 2018-05-29
    Description: Aquaculture in Germany is a small industry, practiced only in a few specifically suited areas. Marine finfish farming is almost nonexistent but mussel farming is a steady activity with a notable level of production. However, this industry is presently very restricted with no hope for expansion as regulations are stringent and new licences in both fresh and marine waters are extremely difficult to obtain. In addition to State-specific conditions within the Federation, the complexity of the regulatory framework is exemplified by focusing on some key aspects for finfish farming and by specific aspects of mussel farming activities in the Schleswig-Holstein Wadden Sea where environmental protection measures dictate the level of control, mainly as a result of the recent establishment of the National Wadden Sea Park.
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  • 38
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    The marine copepod, Pseudocalanus elongatus, as a mediator between climate variability and fisheries in the central Baltic Sea (2003)
    Wiley
    In:  Fisheries Oceanography, 12 . pp. 360-368.
    Details
    Publication Date: 2019-03-06
    Description: Pseudocalanus elongatus is a key species in the pelagic zone of the deep basins of the Central Baltic Sea. The copepod serves as a major food organism for larval as well as for adult, pelagic planktivorous fish. Large interannual fluctuations in the standing stock of P. elongatus have been attributed to significant changes in the hydrographic environment over the last two decades. In particular, the decreasing salinity in the Baltic deep basins, a result of a change in atmospheric forcing leading to an increase in rainfall since the 1980s and of a lack of pulses of saline water intrusions from the North Sea, was found to affect reproduction and maturation of the copepod. In parallel, dramatic changes in the weight-at-age of herring, one of the most important commercial fishes of the Baltic Sea, have been observed since the late 1980s. Using time-series on herring stomach contents, as well as length and weight, we provide evidence for a chain of events relating variability in climate, salinity and P. elongatus abundance to changes in diet and condition of herring in the Central Baltic Sea.
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  • 39
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    Zooplankton interactions in an enclosure experiment (2004)
    Wiley
    In:  Freshwater Biology, 49 . pp. 1495-1504.
    Details
    Publication Date: 2019-09-23
    Description: 1. Density gradients of cladocerans and copepods were generated in an enclosure experiment to compare the impact on the plankton of a filter feeder (Daphnia hyalina × galeata) with that of more selective feeders (calanoid and cyclopoid copepods). The experiment was conducted in situ over 25 days during spring in a mesotrophic lake, Schöhsee, Germany. 2. The plankton community was monitored regularly. Daphniids were able to graze on the phytoplankton present, which mainly consisted of small (〈1000 μm3) species, whereas copepods did not show any impact on algae. 3. At the end of the experiment, Daphnia and remaining cyclopoid copepods were harvested and sorted manually, prior to analyses for stable isotopes of carbon and nitrogen. Daphniids from mesocosms stocked purely with differing densities of Daphnia showed little variability in stable isotope values, whereas those that thrived in enclosure bags together with copepods exhibited lower δ13C values. 4. The change in Daphniaδ13C indicates a change of food sources, modified by the presence of the copepods: the higher the mean abundance of copepods in the enclosures, the more 13C-depleted the daphniids. Increasing abundance of high nucleic acid (HNA) bacteria in the copepod bags may account for the trend in Daphniaδ13C via increased grazing on the bacteria themselves, or via grazing on phytoplankton utilising isotopically light CO2 from respiratory release. 5. Cyclopoid copepod stable isotope signatures were related to Daphnia and copepod abundances in copepod bags, suggesting that cyclopoids preyed on the available zooplankton.
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  • 40
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    Seasonal and interannual variability of Siberian river discharge in the Laptev Sea inferred from stable isotopes in modern bivalves. (2003)
    Wiley
    In:  Boreas, 32 (2). pp. 292-303.
    Details
    Publication Date: 2019-09-23
    Description: Stable oxygen and carbon isotope profiles from modern bivalve shells were investigated in order to reconstruct short-term hydrographical changes in the river-shelf system of the Laptev Sea. Oxygen isotopic profiles obtained from the aragonitic species Astarte borealis exhibit amplitude cycles interpreted as annual hydrographical cycles. These records reflect the strong contrast between summer and winter bottom water conditions in the Laptev Sea. The seasonal variations in δ18O are mainly controlled by the riverine freshwater discharge during summer with 0.5‰ per salinity unit. Corrected for a defined species-dependent fractionation offset of -0.37‰, time-dependent salinity records were reconstructed from these δ18O profiles. They indicate a good correspondence to seasonal hydrographic changes and synoptical data. Persistent trends with shell growth towards more negative δ13C values are observed in all specimens and appear to be related to metabolic changes of the bivalves during ontogeny. In contrast, short-term fluctuations are likely linked to seasonal variabilities of the river water outflow patterns and enhanced phytoplankton productivity during summer. This is corroborated by a clear watermass-related distinction of the various δ13C records made on the basis of water depth and distance from the riverine source.
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  • 41
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    The potential of the advective exchange between the western and eastern Baltic stock early life stages (2001)
    Wiley
    In:  Fisheries Oceanography, 10 . pp. 249-258.
    Details
    Publication Date: 2019-09-24
    Description: In order to clarify mechanisms influencing the reproductive success of Baltic cod (Gadus morhua L.), a modelling exercise was performed to examine the effects of the wind-driven circulation on the transport of early life stages between the western and eastern Baltic. Because the different stocks spawn in different areas and environments at different times of the year, the occurrence of variable age/length distributions of juveniles within the different potential nursery areas can be explained by the circulation pattern. A three-dimensional circulation model of the Baltic was utilized to investigate the temporal evolution of egg and larval distributions of the western Baltic cod stock, which spawns preferentially in the Danish Straits, in Kiel Bay as well as in Mecklenburg Bay. For different scenarios (1988 and 1993), within- and between-year variability of egg and larval transport showed large differences, primarily due to variations in wind forcing. In 1988, relatively low and variable wind forcing prevailed, whereas, due to sustained strong, mainly westerly, winds, in January 1993, the recent major Baltic inflow to the Baltic Sea occurred. Differences in contributions of early life stages from the western to the eastern cod stocks, depending on the physical forcing conditions, suggest that this process can be controlled by variations of atmospheric forcing conditions. The potential for early life stages from the western Baltic cod stock to drift into the Arkona Basin and the Bornholm Basin, and to contribute there to the juvenile population, has been recognized as being mainly due to strong westerly winds. During cold winters, retention of eggs, larvae and juveniles within their original spawning grounds may predominate. Transport of cod early life stages from the Øresund, as well as from the Great Belt, can occur only during periods of strong westerly winds, but significant eastwards orientated drift from Kiel Bay and Mecklenburg Bay was also evident during periods of minor westerly wind influence.
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  • 42
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    Seismic images and magnetic signature of the Late Jurassic to Early Cretaceous Africa-Eurasia plate boundary off SW Iberia (2004)
    Wiley
    In:  Geophysical Journal International, 158 . pp. 554-568.
    Details
    Publication Date: 2018-07-17
    Description: Over the last two decades numerous studies have investigated the structure of the west Iberia continental margin, a non-volcanic margin characterized by a broad continent–ocean transition (COT). However, the nature and structure of the crust of the segment of the margin off SW Iberia is still poorly understood, because of sparse geophysical and geological data coverage. Here we present a 275-km-long multichannel seismic reflection (MCS) profile, line AR01, acquired in E–W direction across the Horseshoe Abyssal Plain, to partially fill the gap of information along the SW Iberia margin. Line AR01 runs across the inferred plate boundary between the Iberian and the African plates during the opening of the Central Atlantic ocean. The boundary separates crust formed during or soon after continental rifting of the SW Iberian margin from normal seafloor spreading oceanic crust of the Central Atlantic ocean. Line AR01 has been processed and pre-stack depth migrated to show the tectonic structure of the crust across the palaeo plate boundary. This boundary is characterized by a 30–40-km-wide zone of large basements highs related to landward-dipping reflections, which penetrate to depths of 13–15 km, and it marks a change in the character of the basement structure and relief from east to west. In this study, we have used pre-stack depth migrated images, the velocity model of line AR01 and magnetic data available in the area to show that the change in basement structure occurs across the fossil plate boundary, separating African oceanic crust of the M series (M21–M16) to the west from the transitional crust of the Iberian margin to the east.
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  • 43
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    Crustal structure of the Peruvian continental margin from wide-angle seismic studies (2004)
    Wiley
    In:  Geophysical Journal International, 158 (2). pp. 749-764.
    Details
    Publication Date: 2018-07-17
    Description: Active seismic investigations along the Pacific margin off Peru were carried out using ocean bottom hydrophones and seismometers. The structure and the P-wave velocities of the obliquely subducting oceanic Nazca Plate and overriding South American Plate from 8°S to 15°S were determined by modelling the wide-angle seismic data combined with the analysis of reflection seismic data. Three detailed cross-sections of the subduction zone of the Peruvian margin and one strike-line across the Lima Basin are presented here. The oceanic crust of the Nazca Plate, with a thin pelagic sediment cover, ranging from 0–200 m, has an average thickness of 6.4 km. At 8°S it thins to 4 km in the area of Trujillo Trough, a graben-like structure. Across the margin, the plate boundary can be traced to 25 km depth. As inferred from the velocity models, a frontal prism exists adjacent to the trench axis and is associated with the steep lower slope. Terrigeneous sediments are proposed to be transported downslope due to gravitational forces and comprise the frontal prism, characterized by low seismic P-wave velocities. The lower slope material accretes against a backstop structure, which is defined by higher seismic P-wave velocities, 3.5–6.0 km s−1. The large variations in surface slope along one transect may reflect basal removal of upper plate material, thus steepening the slope surface. Subduction processes along the Peruvian margin are dominated by tectonic erosion indicated by the large margin taper, the shape and bending of the subducting slab, laterally varying slope angles and the material properties of the overriding continental plate. The erosional mechanisms, frontal and basal erosion, result in the steepening of the slope and consequent slope failure.
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  • 44
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    Variability in condition and growth of Atlantic cod larvae and juveniles reared in mesocosms: environmental and maternal effects (2003)
    The Fisheries Society of the British Isles | Wiley | Blackwell
    In:  Journal of Fish Biology, 62 . pp. 706-723.
    Details
    Publication Date: 2019-08-08
    Description: Standard length, dry mass and RNA : DNA ratio measurements of 3876 Atlantic cod Gadus morhua larvae and juveniles from 26 families of recruit (fish during their first year of spawning) and repeat spawners (fish which were in their subsequent spawning season) reared in two mesocosms (2500 and 4400 m3) under semi-natural conditions were analysed over a period of 10 weeks using microsatellites. Larvae from recruit spawners were significantly longer and heavier at hatch and throughout the 10 weeks. RNA : DNA ratios from recruit spawner offspring were only significantly higher at week 1. The smaller (2500 m3) mesocosm was characterized by low plankton density during the transition from endogenous to exogenous feeding followed by a higher density during the metamorphosis period (weeks 4 and 5), with the reverse pattern evident in the 4400 m3 mesocosm. Patterns of larval growth followed patterns of zooplankton density. Significant differences in RNA : DNA ratios between the mesocosms at all comparable sampling dates were found and within each mesocosm individual fish exhibited a wide range of growth and condition responses under the same environmental conditions. RNA : DNA ratios as a function of size differed in the amount of variability between mesocosms, indicating that the higher food density led to a higher proportion of well-conditioned larvae in the first 3 weeks. Food availability probably has a major role in determining offspring growth and condition, with limited effects due to maternal effects in cases where the broodstock females are approximately of similar size and condition.
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  • 45
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    Three-dimensional seismic refraction tomography of the crustal structure at the ION site on the Ninetyeast Ridge, Indian Ocean (2003)
    Wiley
    In:  Geophysical Journal International, 152 (1). pp. 171-184.
    Details
    Publication Date: 2018-07-17
    Description: We have performed a 3-D seismic refraction tomography of a 48 × 48 km2 area surrounding ODP site 757, which is planned to host an International Ocean Network (ION) permanent seismological observatory, called the Ninetyeast Ridge Observatory (NERO). The study area is located in the southern part of the Ninetyeast Ridge, the trail left by the Kerguelen hotspot on the Indian plate. The GEOMAR Research Centre for Marine Geosciences and the Federal Institute for Geosciences and Natural Resources acquired 18 wide-angle profiles recorded by 23 ocean bottom hydrophones during cruise SO131 of R/V Sonne in spring 1998. We apply a first arrival traveltime tomography technique using regularized inversion to recover the 3-D velocity structure relative to a 1-D background model that was constructed from a priori information and averaged traveltime data. The final velocity model revealed the crustal structure down to approximately 8 km depth. Resolution tests showed that structures with approximately 6 km horizontal extent can reliably be resolved down to that depth. The survey imaged the extrusive layer of the upper crust of the Ninetyeast Ridge, which varies in thickness between 3 and 4 km. A high-velocity anomaly coinciding with a positive magnetic anomaly represents a volcanic centre from which crust in this area is thought to have formed. A pronounced low-velocity anomaly is located underneath a thick sedimentary cover in a bathymetric depression. However, poor ray coverage of the uppermost kilometre of the crust in this area resulted in smearing of the shallow structure to a larger depth. Tests explicitly including the shallow low-velocity layer confirmed the existence of the deeper structure. The heterogeneity of the upper crust as observed by our study will have consequences for the waveforms of earthquake signals to be recorded by the future seismic observatory.
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  • 46
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    Copepods act as switch between alternative trophic cascades in marine pelagic food webs (2004)
    Wiley
    In:  Ecology Letters, 7 (4). pp. 321-328.
    Details
    Publication Date: 2019-09-23
    Description: A recent meta-analysis indicates that trophic cascades (indirect effects of predators on plants via herbivores) are weak in marine plankton in striking contrast to freshwater plankton (Shurin et al. 2002, Ecol. Lett., 5, 785–791). Here we show that in a marine plankton community consisting of jellyfish, calanoid copepods and algae, jellyfish predation consistently reduced copepods but produced two distinct, opposite responses of algal biomass. Calanoid copepods act as a switch between alternative trophic cascades along food chains of different length and with counteracting effects on algal biomass. Copepods reduced large algae but simultaneously promoted small algae by feeding on ciliates. The net effect of jellyfish on total algal biomass was positive when large algae were initially abundant in the phytoplankton, negative when small algae were dominant, but zero when experiments were analysed in combination. In contrast to marine systems, major pathways of energy flow in Daphnia-dominated freshwater systems are of similar chain length. Thus, differences in the length of alternative, parallel food chains may explain the apparent discrepancy in trophic cascade strength between freshwater and marine planktonic systems.
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  • 47
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    Body size determines the strength of the latitudinal diversity gradient (2001)
    Wiley
    In:  Ecography, 24 (3). pp. 251-256.
    Details
    Publication Date: 2016-12-21
    Description: In most groups of organisms, the species richness decreases from the tropics to the poles. The mechanisms causing this latitudinal diversity gradient are still controversial. We present data from a comprehensive weighted meta-analysis on the strength of the latitudinal gradient in relation to body size. We sampled literature data on the correlation between species richness and latitude for a variety of organisms, ranging from trees to protozoa. In addition, own data on the presence of large-scale diversity patterns for diatoms were included, both for local and regional species richness. The strength of the latitudinal gradient was positively correlated to the size of the organisms. Strongest decreases of species richness to the poles was found for large organisms like trees and vertebrates, whereas meiofauna, protozoa and diatoms showed weak or no correlations between species richness and latitude. These results imply that latitudinal gradients are shaped by non-equilibrium (regional) processes and are persistent under conditions of dispersal limitation.
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  • 48
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    Breeding teeth in Atlantic salmon: fact or fake? (2004)
    Wiley
    In:  Journal of Morphology, 260 . pp. 340-341.
    Details
    Publication Date: 2018-04-03
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  • 49
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    Empirical relationships to estimate asymptotic length, length at first maturity and length at maximum yield per recruit in fishes, with a simple method to evaluate length frequency data (2000)
    The Fisheries Society of the British Isles | Wiley
    In:  Journal of Fish Biology, 56 . pp. 758-773.
    Details
    Publication Date: 2019-08-08
    Description: Empirical relationships are presented to estimate in fishes, asymptotic length (L∞) from maximum observed length (Lmax), length at first maturity (Lm) from L∞, life span (tmax) from age at first maturity (tm), and length at maximum possible yield per recruit (Lopt) from L∞ and from Lm, respectively. The age at Lopt is found to be a good indicator of generation time in fishes. A spreadsheet containing the various equations can be downloaded from the Internet at http://www.fishbase.org/download as popdynJFB.zip. A simple method is presented for evaluation of length–frequency data in their relationship to L∞, Lm and Lopt. This can be used to evaluate the quality of the length–frequency sample and the status of the population. Three examples demonstrate the usefulness of this method. 2000 The Fisheries Society of the British Isles
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  • 50
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    Patterns of tooth replacement in osteichthyans: variations on a theme (2004)
    Wiley
    In:  Journal of Morphology, 260 . p. 301.
    Details
    Publication Date: 2018-04-03
    Description: Nonmammalian tooth-bearing vertebrates usually replace their teeth throughout life. Much about how a replacement pattern is generated has been learned from zebrafish. However, to understand general mechanisms of tooth replacement, advantage can be taken from studying other, “nonmodel” species. We have mapped the patterns of tooth replacement in widely divergent aquatic osteichthyans using 2D charts, in which one axis is time, the other linear spacing along the tooth row. New teeth that are generated simultaneously are considered part of the same odontogenic wave. Using this approach, it appears that a similar, general pattern underlies very distinctive dentitions in distantly related species. A simple shift in spacing of odontogenic waves, or in distance between subsequent tooth positions along a row (or both), can produce dramatically different dentitions between life stages within a species, or between closely related species. Examples will be presented from salmonids, cyprinids, and cichlids. Our observations suggest that lines linking subsequent positions may have more biological significance than replacement waves (usually linking alternate positions), often used to explain the generation of patterns. The presence of a general pattern raises questions about common control mechanisms. There is now increasing evidence, at least for the zebrafish, to support a role for stem cells in continuous tooth renewal and control of replacement patterns.
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  • 51
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    Geometry of extensional faults developed at slow-spreading centres from seismic reflection data in the Central Atlantic (Canary Basin) (2004)
    Wiley
    In:  Geophysical Journal International, 159 . pp. 591-606.
    Details
    Publication Date: 2018-07-17
    Description: We present depth images, from portions of profiles that are close to flow-lines, of Cretaceous oceanic crust in the eastern Central Atlantic. Compared with post-stack time migrations, the images illustrate the improvement resulting from the application of pre-stack depth migration. The images document the scale and geometry of normal faulting in oceanic crust formed over 25 Myr at a half-spreading rate of less than 10 mm yr−1, and the variation in extensional style with position within the spreading segment. Away from major fault zones (FZs), most faults are subplanar, dip more than 35°, are associated with moderate basement relief (0.2–1 km relief) and may penetrate to deep crustal levels. These faults could be related to the lifting of the lithosphere out of the median valley to the flanking mountains. Also observed away from FZs are gently dipping to subhorizontal reflections in the upper crust, which resemble detachment faults. In contrast, the inside corner crust is more rugged, with basement highs rising up to 2 km above the intervening basins. This larger-scale topography is associated with a different style of faulting: the depth images reveal gently dipping (〈35°) faults that are rooted in the deep crust and that project to the ridgeward flank of the dome-shaped large basement highs (1–2 km vertical relief). The faults seem to continue as the ridge-facing flank of these highs and some may extend over the crest of the high to breakaways beyond. In this case, the domal highs that form the exhumed footwall to the faults can be described as oceanic core complexes. These controlling faults are up to 20 km long and have a heave of ∼10 km, sufficient to have accommodated up to 50 per cent extension and to have exhumed deep crustal and perhaps even mantle rocks. We suggest that similar faults can explain the structure and lithologies found at megamullion structures (oceanic core complexes) at inside corners near the present-day spreading ridge.
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  • 52
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    North Atlantic Oscillation signatures in ecosystems - a meta-analysis (2002)
    Wiley
    In:  Global Change Biology (8). pp. 203-212.
    Details
    Publication Date: 2018-05-16
    Description: Climate variations over the Northern Hemisphere are to a substantial proportion associated with the North Atlantic Oscillation (NAO). Recently, many studies revealed the impacts of the NAO on the dynamics of organisms in different ecosystems but the results in the single studies were inconsistent. Here, we used meta‐analysis techniques for a quantitative synthesis of results. We tested the influence of the NAO on the timing of life history events, on biomass of organisms, and on biomass of different trophic levels. We found a clear NAO signature in freshwater, marine, and terrestrial ecosystems. The response of life history events to the NAO was similar in all environments but less pronounced at higher latitudes. The magnitude of the biomass response was significantly related to the NAO, either positively in aquatic or negatively in terrestrial ecosystems. The response depended on longitude, the effect being less pronounced in Eastern Europe. The results stressed that a meta‐analysis is a valuable tool in the field of climate‐driven ecosystem responses and can identify more general ecological responses than single studies. We recommend the inclusion of nonsignificant results in order to archive an objective view of the strength of NAO and climate impacts in general.
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  • 53
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    Daphnia population growth but not moulting is a substantial phosphorus drain for phytoplankton (2003)
    Wiley
    In:  Freshwater Biology, 48 (1). pp. 67-74.
    Details
    Publication Date: 2017-01-10
    Description: 1. Negative effects of zooplankton on the availability of phosphorus (P) for phytoplankton as a result of the retention of nutrients in zooplankton biomass and the sedimentation of exoskeletal remains after moulting, have been recently proposed. 2. In a mesocosm study, the relative importance of these mechanisms was tested for the freshwater cladoceran Daphnia hyalina×galeata. A total of 13 mesocosm bags was suspended in a mesotrophic German lake during summer 2000 and fertilised with inorganic P in order to obtain a total nitrogen to total P ratio closer to the Redfield ratio. D. hyalina×galeata was then added at a logarithmically scaled density gradient of up to 40 ind. L−1. Zooplankton densities, dissolved inorganic, particulate organic (seston 〈100 μm), as well as total nutrient concentrations were monitored. Additionally, nutrient concentrations of sediment water removed from the bottom of the mesocosm bags via a manual pump were determined. 3. Seston carbon (C), seston P and total P were significantly negatively correlated with Daphnia densities. The amount of particulate P (∼5–6 μg P L−1) sequestered from the seston compartment by Daphnia corresponded roughly to the increase of zooplankton biomass (population growth). Soluble reactive phosphorous (SRP) was at all times high (∼25–35 μg P L−1) and possibly unavailable to phytoplankton as a result of P adsorption to calcite during a calcite precipitation event (whiting). P concentrations determined in sediment water were generally 〈60 μg P m−2 and thus never exceeded 1% of the total amount of P bound in particulate matter of the overlying water column. 4. Seston C : P ratios followed a polynomial second-order function: At Daphnia densities 〈40 ind. L−1 a positive linear relationship was evident, which is explained by the stronger reduction of P compared with C in seston, and transfer of seston P to zooplankton. Highest seston C : P ratios of ∼300 : 1 were observed at Daphnia densities of ∼30–50 ind. L−1, which is in agreement with proposed threshold values limiting Daphnia reproductive growth. At Daphnia densities 〉40–50 ind. L−1 C : P ratios were decreased because of the strong reduction of seston C at close to constantly low seston P-values of ∼3–4 μg P L−1. 5. At least for Daphnia, it may be concluded that – unlike population growth – the sedimentation of faecal pellets and carapaces after moulting seem negligible processes in pelagic phosphorus dynamics.
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  • 54
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    Radar Doppler velocity of volcanic eruptions: Theoretical considerations and quantitative documentation of changes in eruptive behaviour at Stromboli volcano, Italy (2003)
    Wiley
    In:  Geophysical Journal International, 154 (2). pp. 515-532.
    Details
    Publication Date: 2018-07-17
    Description: The use of radar Doppler velocimetry for the observation of volcanic activity is new. We used this method to continuously observe the activity of one vent of Stromboli volcano, Italy, from the end of 2000 April until early May. During this period we recorded 702 eruptions, 132 of which occurred before a strong rain storm passed over the island on April 29. In order to interpret the recorded Doppler data we developed a program that simulates different strombolian eruption scenarios, for which we then calculate the theoretical Doppler spectra. Comparing our theoretical data with the observed data we are able to show that most of the eruptions are nearly vertical, although we did observe only one component of the eruption vector with our Doppler radar. One of the most interesting features of the data set is a significant change in eruptive behaviour that correlates with the occurrence of the rain storm: we find that on average the eruption duration increased by a factor of 2, eruptive velocities were much higher and indirect evidence indicates that the average particle diameter of the erupted material decreased. This change may have several causes, but the coincidence with the rain storm may be evidence of magma–water interaction and feedback on the volcanic activity. If the fluid source (rain) changing the eruptive style is at the surface and in near-surface layers then the main control on final eruption dynamics at Stromboli volcano must also be in rather shallow regions.
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  • 55
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    Fluctuation of zooplankton taxa in ballast water during short-term and long-term ocean-going voyages (2000)
    Wiley
    In:  International Review of Hydrobiology, 85 (5-6). pp. 597-608.
    Details
    Publication Date: 2017-05-30
    Description: A major vector for unintentional species introductions is international shipping. A wide range of organisms have been transported over long distances in ships' ballast tanks and as hull fouling. Although many desk studies and ship sampling programmes have been carried out, little information is available on changing numbers of individuals in ballast water during voyages. Detailed information could assist in evaluating the dimension of species import and future risks of unintentional species introductions by ballast water. The first European study, organised as a concerted action team and financed by the European Union, carried out several long-term and short-term workshops on board ships undertaking international voyages. The preliminary results from sampling the ballast water of the first four oceangoing workshops of this Concerted Action showed a decrease in numbers of specimens and taxa over time.
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  • 56
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    Changes in bacterial abundance and community structure in cage fish‐culture caused by water turbulence during feeding (2000)
    Wiley
    In:  Journal of Applied Ichthyology, 16 (1). pp. 27-31.
    Details
    Publication Date: 2018-05-29
    Description: Water and sediment quality conditions in and around a cage culture unit located in Wismar Bay (Western Baltic Sea, Germany) were investigated during summer 1994 using bacterial group indicators (Enterobacteriaceae, saprophytic bacteria and Vibrio, determined on selective media). Fish were fed once daily with extruded commercial pellets. Over a period of 8 days samples were taken before and after feeding at different sampling points close to or at the cages. The results showed that a drastic (up to 10 times) increase in different bacterial groups occurred inside the cages 10 min after feeding as well as occasionally in the surrounding water. Additional electron-microscopic observations of the bacterial biofilm on the cage nets revealed that a decrease (in comparison with the original number) in total bacteria on the net materials of 9.5 up to 42.8% occurred after feeding. It was concluded that water mixing caused by frenzied swimming just before and during feeding caused a release of bacteria which were growing vigorously on the surfaces of the cage system. Since the pathogenity and hydrophobicity of bacteria are closely related, this process of redistribution of bacteria into the water column could constitute an important stress factor for fish, which could probably also have a negative effect on fish production.
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  • 57
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    UV effects that come and go: A global comparison of marine benthic community level impacts. (2004)
    Wiley
    In:  Global Change Biology, 10 (12). pp. 1962-1972.
    Details
    Publication Date: 2018-05-16
    Description: Ambient UV radiation has substantially increased during the last decades, but its impact on marine benthic communities is hardly known. The aim of this study was to globally compare and quantify how shallow hard-bottom communities are affected by UV during early succession. Identical field experiments in 10 different coastal regions of both hemispheres produced a consistent but unexpected pattern: (i) UV radiation affected species diversity and community biomass in a very similar manner, (ii) diversity and biomass were reduced to a larger extent by UVA than UVB radiation, (iii) ambient UV levels did not affect the composition of the communities, and (iv) any UV effects disappeared during species succession after 2–3 months. Thus, current levels of UV radiation seem to have small, predictable, and transient effects on shallow marine hard-bottom communities.
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  • 58
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    Ecophysiological traits explain species dominance patterns in macroalgal blooms (2000)
    Wiley
    In:  Journal of Phycology (36). pp. 287-295.
    Details
    Publication Date: 2018-04-26
    Description: Macroalgal blooms are a growing environmental problem in eutrophic coastal ecosystems world wide. These blooms are dominated typically by only one out of several co‐occurring opportunistic species, which are all favored by increased nutrient loads. We asked whether pronounced dominance of filamentous Pilayella littoralis Kjellm. (Phaeophyceae) over foliose Enteromorpha intestinalis L. (Chlorophyceae) in the Baltic Sea can be explained by interspecific physiological differences. In laboratory experiments, we analyzed uptake kinetics of nitrate, ammonium, and phosphate and the time dependency of uptake rates for both species. We further examined growth rates and nutrient assimilation in relation to single and combined enrichment with nitrate and phosphate, and three different nitrogen sources. Overall, we did not detect distinct differences in uptake, growth, and assimilation rates between P. littoralis and E. intestinalis. Minor differences and the related advantages for single species are discussed. Highest maximal uptake rates were found for ammonium, followed by nitrate and phosphate. Strong time dependency of uptake occurred, with the highest rates during the first 15 to 30 min. Nitrate enrichment had far more of an effect on growth than phosphate. Enrichment with urea, ammonium, and nitrate significantly increased growth rates without interspecific differences. A larger surface area to volume (SA/V) ratio in Pilayella compared with Enteromorpha did not translate into greater physiological capacity. We conclude that species dominance patterns in macroalgal blooms are not always a direct result of different ecophysiological traits among species. Ecological traits such as susceptibility to herbivory are important factors in determining species distribution in the field.
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  • 59
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    Phytoplankton diversity of shallow tidal lakes: influence of periodic salinity changes on diversity and species number of a natural assemblage (2004)
    Wiley
    In:  Journal of Phycology, 40 . pp. 54-61.
    Details
    Publication Date: 2018-05-30
    Description: The influence of periodic salinity changes was investigated for 42 days under semicontinuous culture conditions with phosphorus limitation using phytoplankton assemblages from Lake Waihola, a tidally influenced shallow lake. To simulate tidal effects on the phytoplankton community, salinity in the cultures was increased in pulses at different intervals (3.5, 7, and 14 days), and these cultures were compared with those that experienced constant freshwater conditions. Salinity pulses significantly affected competition and succession with a major loss in diversity during the first days of the experiment due to the initial pulse that caused a transition from freshwater to brackish conditions in the cultures. After this initial phase, diversity index (H') and species number (Scorr) decreased less rapidly. The loss in H' and Scorr over time was highest under constant freshwater conditions and lowest in the treatment with an interval of 3.5 days between salinity pulses. At the end of the experiment, the combination of initial loss in H' and Scorr and the time course of H' and Scorr resulted in a U‐shaped relation between the interval length of salinity pulses and both H' and Scorrtemp1.txttemp1.txt. Our results indicate that salinity pulses at intervals of a few days tend to promote phytoplankton diversity. If saline intrusions in coastal freshwater systems occur only at spring tides, this will lead to decreases in diversity and species richness.
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  • 60
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    The reaction of young coho Oncorhynchus kisutch to declining oxygen levels during long-term exposure (2000)
    Wiley
    In:  Journal of Applied Ichthyology, 16 . pp. 14-19.
    Details
    Publication Date: 2017-06-23
    Description: The respiration of coho salmon, Oncorhynchus kisutch, weighing between 20 and 45 g was measured at gradually declining oxygen levels and at temperatures ranging between 14 and 17 °C. The maximum and minimum oxygen concentrations tested were 235 and 41 μmol/L, respectively. Respiration rates were measured for 24 h at 235 μmol/L before the oxygen concentration was lowered stepwise to 157 and 81 μmol/L. In one single trial, the oxygen level was lowered to 66, 53, and 41 μmol/L. Respiration was highly variable in time. Peak activities always occurred during the night. The standard metabolic rate at normoxic conditions was estimated to be around 4 μmol oxygen/g/h. The highest rates reached values close to 15 μmol oxygen/g/h. At reduced oxygen levels the standard oxygen demand slightly increased to 4.5 μmol oxygen/g/h, indicating a higher demand for vital metabolic functions. Due to the decrease of swimming activity, the maximum oxygen uptake rates dropped to 〈 8 μmol oxygen/g/h below 81 μmol/L oxygen concentration. Under long-term conditions, physiological and behavioural adaptations play an important role for survival and need to be considered for the design and operation of fish farm facilities.
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    A Signal Released by an Endophytic Attacker Acts as a Substrate for a Rapid Defensive Reaction of the Red Alga Chondrus crispus (2002)
    Chemistry Europe | Wiley
    In:  ChemBioChem, 3 (12). pp. 1260-1263.
    Details
    Publication Date: 2020-07-27
    Description: A backfiring weapon: The release of H2O2 by an amino acid oxidase is the early defensive reaction of the red alga Chondrus crispus against the endophytic green algal pathogen Acrochaete operculata (see scheme). This reaction can be induced by L-asparagine, which is released by the attacker when it recognises host cell-wall κ-carrageenan oligosaccharides. The induced signal of the attacker thus serves directly as the substrate for the production of the defensive metabolite.
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  • 62
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    Two new triterpene and a new nortriterpene glycosides from Phlomis viscosa (2004)
    Wiley
    In:  Helvetica Chimica Acta, 87 (3). pp. 611-619.
    Details
    Publication Date: 2020-07-29
    Description: The isolation and structure elucidation of two new oleanane-type triterpene glycosides, 29-(β-D-glucopyranosyloxy)-2α,3β,23-trihydroxyolean-12-en-28-oic acid (=(2α,3β,4α,29α)-29-(β-D-glucopyranosyloxy)-2,3,23-trihydroxyolean-12-en-28-oic acid; 1) and its C(20)-epimer, 30-(β-D-glucopyranosyloxy)-2α,3β,23-trihydroxyolean-12-en-28-oic acid (=(2α,3β,4α,29β)-29-β-D-glucopyranosyloxy)-2,3,23-trihydroxyolean-12-en-28-oic acid; 2), and a novel nortriterpene glycoside, (17S)-2α,18β,23-trihydroxy-3,19-dioxo-19(18[RIGHTWARDS ARROW]17)- abeo-28-norolean-12-en-25-oic acid β-D-glucopyranosyl ester (=(1R,2S,4aS,4bR,6aR,7R,9R,10aS,10bS)-3,4,4a,4b,5,6,6a,7,8,9,10,10a,10b,11-tetradecahydro-1-hydroxy-7-(hydroxymethyl)-3′,4′,4a,4b,7-pentamethyl-2′,8- dioxospiro[chrysene-2(1H),1′-cyclopentane]-10a-carboxylic acid β-D-glucopyranosyl ester; 3) from Phlomis viscosa (Lamiaceae) are reported. The structures of the compounds were asigned by means of spectroscopic (IR, 1D- and 2D-NMR, and LC-ESI-MS) and chemical (acetylation) methods.
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  • 63
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    Response of Gracilaria conferta (Rhodophyta) to oligoagars results in defense against agar-degrading epiphytes (2000)
    Wiley
    In:  Journal of Phycology, 36 (6). pp. 1079-1086.
    Details
    Publication Date: 2020-07-20
    Description: Elicitation of Gracilaria conferta (Schousboe ex Montagne) J. ct G. Feldmann with oligoagars resulted in a defense response that was strong enough to kill epiphytic bacteria associated with the alga. Up to 60% of the resident bacterial flora of healthy plants was eliminated within 60 min after addition of neoagarohexaose to the algal medium. Single isolates of agar-degrading bacteria that had been isolated previously from healthy or decaying algal tissues proved to be more sensitive, Some of them were generally unable to survive on healthy G, conferta. Others survived on unelicited plants. Approximately 90% of these more resistant agar degraders were eliminated within 15 min after elicitation. The bacterial degradation of dead tissue of G, conferta resulted in a release of elicitors. The elicitors accumulated in the medium and reached high enough concentrations within 24 h to induce a hypersensitive response in healthy algae, The eliciting agent could be destroyed with beta -agarase and was thus probably oligoagar, Application of antibiotics prevented the accumulation of the elicitor, which indicated that bacteria were responsible for its release from the algal biomass, The hypersensitive response of G. conferta after contact with oligoagars is thus a true defense response, because it enables the plant to protect itself efficiently from enzymatic attacks on its cell wall.
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  • 64
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    Further rock magnetic and chronostratigraphic results on reversal excursions during the last 50 ka as derived from northern high latitudes and discrepancies in precise AMS14C dating (2003)
    Wiley
    In:  Geophysical Journal International, 155 (3). pp. 1065-1080.
    Details
    Publication Date: 2019-09-23
    Description: A total of five sediment cores from three sites, the Arctic Ocean, the Fram Strait and the Greenland Sea, yielded evidence for geomagnetic reversal excursions and associated strong lows in relative palaeointensity during oxygen isotope stages 2 and 3. A general similarity of the obtained relative palaeointensity curves to reference data can be observed. However, in the very detail, results from this high‐resolution study differ from published records in a way that the prominent Laschamp excursion is clearly characterized by a significant field recovery when reaching the steepest negative inclinations, whereas only the N–R and R–N transitions are associated with the lowest values. Two subsequent excursions also reach nearly reversed inclinations but without any field recovery at that state. A total of 41 accelerator mass spectrometry (AMS) 14C ages appeared to allow a better age determination of these three directional excursions and related relative palaeointensity variations. However, although the three sites yielded more or less consistent chronological as well as palaeomagnetic results a comparison to another site, PS2644 in the Iceland Sea, revealed significant divergences in the ages of the geomagnetic field excursions of up to 4 ka even on basis of uncalibrated AMS 14C ages. This shift to older 14C ages cannot be explained by a time‐transgressive character of the excursions, because the distance between the sites is small when compared with the size of and the distance to the geodynamo in the Earth's outer core. The most likely explanation is a difference of reservoir ages and/or mixing with old 14C‐depleted CO2 from glacier ice expelled from Greenland at site PS2644.
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  • 65
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    Growth regulation of rRNA content in Prochlorococcus and Synechococcus (Marine Cyanobacteria) measured by whole-cell hybridization of rRNA-targeted peptide nucleic acids (2003)
    Wiley
    In:  Journal of Phycology, 39 (3). pp. 527-534.
    Details
    Publication Date: 2019-03-06
    Description: The cyanobacteria Synechococcus and Prochlorococcus are important primary producers in marine ecosystems. Because currently available approaches for estimating microbial growth rates can be difficult to apply in the field, we have been exploring the feasibility of using quantitative rRNA measurements as the basis for making such estimates. In this study we examined the relationship between rRNA and growth rate in several Synechococcus and Prochlorococcus strains over a range of light-regulated growth rates. Whole-cell hybridization with fluorescently labeled peptide nucleic acid (PNA) probes was used in conjunction with flow cytometry to quantify rRNA on a per cell basis. This PNA probing technique allowed rRNA analysis in a phycoerythrin-containing Synechococcus strain (WH7803) and in a non-phycoerythrincontaining strain and in Prochlorococcus. All the strains showed a qualitatively similar tri-phasic relationship between rRNA·cell-1 and growth rate, involving relatively little change in rRNA·cell-1 at low growth rates, linear increase at intermediate growth rates, and a plateau and/or decrease at the highest growth rates. The onset of each phase was associated with the relative, rather than absolute, growth rate of each strain. In the Synechococcus strains, rRNA normalized to flow cytometrically measured forward angle light scatter (an indicator of size) was well-correlated with growth rate across strains. These findings support the idea that cellular rRNA may be useful as an indicator of in situ growth rate in natural Synechococcus and Prochlorococcus populations.
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  • 66
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    The influence of seasonal environmental changes on ontogenetic migrations of the squid Loligo gahi on the Falkland shelf (2004)
    Wiley
    In:  Fisheries Oceanography, 13 (1). pp. 1-9.
    Details
    Publication Date: 2021-07-14
    Description: The Patagonian longfin squid Loligo gahi undertakes horizontal ontogenetic migrations on the Falkland shelf: juveniles move from spawning grounds located in shallow, inshore waters (20–50 m depths) to feeding grounds near the shelf edge (200–350 m depths). Immature squid feed and grow in these offshore feeding grounds and, upon maturation, migrate back to inshore waters to spawn. The possible influence of environmental factors on L. gahi migrations was investigated using data from oceanographic transects, crossing the region of known L. gahi occurrence. They were made from the inshore waters of East Falkland eastwards to depths of 1250 m on a monthly basis from 1999 to 2001. Four main water types were found in the region: Shelf, Sub-Antarctic Superficial and Antarctic Intermediate water masses, and Transient Zone waters. The inshore spawning grounds occur in the Shelf Water mass, whereas the feeding squid (medium-sized immature and maturing individuals) were associated with the Transient Zone. The 5.5°C isotherm appeared to mark the limit of squid distribution into deeper waters in all seasons. Seasonal changes in water mass characteristics and location were found to be important for seasonal changes in L. gahi migrations on the Falkland shelf.
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  • 67
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    Reproductive system of the giant squid Architeuthis in South African waters (2004)
    Wiley
    In:  Journal of Zoology, 264 (2). pp. 153-169.
    Details
    Publication Date: 2021-09-07
    Description: The reproductive system is described from 15 giant squid Architeuthis sp., collected between 1972 and 2002 in South African waters. Distinctive features of the male reproductive system are the long muscular terminal organ, with elaboration of the anterior end, and modification of the tips of the ventral arms, probably hectocotilization. The spermatophoric organ has a long finishing gland that extends from the base of the gill. The terminal organ is differentiated internally into three distinct parts, involved in the guidance, storage, protection, expulsion and possibly the coating of spermatophores. Length of spermatophores in the terminal organ varied considerably. Several stages of spermatophores were found, from tentative to false to fully formed spermatophores, within a single animal. Distinctive features of the female reproductive system are a mesentery surrounding the main blood vessels of the ovary and attaching the ovary to the dorsal gladius chamber, multiple branching (at least three times) of the genital aorta that supplies the developing oocytes, high potential fecundity (3.5–6.2 ± 106 oocytes), small eggs and short oviducts that suggest intermittent (extended) spawning. Large concentrations and single spermatangia were found in various places in females, indicating non-specific deposition. The transfer of spermatophores is probably rapid, perhaps because of considerable sexual size dimorphism (at maturity, males are much smaller than females). Implants in males are probably self-induced since the majority were found within reach of the terminal organ opening (primarily on the ventral arms in males).
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  • 68
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    Aposymbiotic culture of the sepiolid squidEuprymna scolopes: Role of the symbiotic bacteriumVibrio fischeri in host animal growth, development, and light organ morphogenesis (2000)
    Wiley
    In:  The Journal of Experimental Zoology, 286 (3). pp. 280-296.
    Details
    Publication Date: 2021-06-28
    Description: The sepiolid squid Euprymna scolopes forms a bioluminescent mutualism with the luminous bacterium Vibrio fischeri, harboring V. fischeri cells in a complex ventral light organ and using the bacterial light in predator avoidance. To characterize the contribution of V. fischeri to the growth and development of E. scolopes and to define the long-term effects of bacterial colonization on light organ morphogenesis, we developed a mariculture system for the culture of E. scolopes from hatching to adulthood, employing artificial seawater, lighting that mimicked that of the natural environment, and provision of prey sized to match the developmental stage of E. scolopes. Animals colonized by V. fischeri and animals cultured in the absence of V. fischeri (aposymbiotic) grew and survived equally well, developed similarly, and reached sexual maturity at a similar age. Development of the light organ accessory tissues (lens, reflectors, and ink sac) was similar in colonized and aposymbiotic animals with no obvious morphometric or histological differences. Colonization by V. fischeri influenced regression of the ciliated epithelial appendages (CEAs), the long-term growth of the light organ epithelial tubules, and the appearance of the cells composing the ciliated ducts, which exhibit characteristics of secretory tissue. In certain cases, aposymbiotic animals retained the CEAs in a partially regressed state and remained competent to initiate symbiosis with V. fischeri into adulthood. In other cases, the CEAs regressed fully in aposymbiotic animals, and these animals were not colonizable. The results demonstrate that V. fischeri is not required for normal growth and development of the animal or for development of the accessory light organ tissues and that morphogenesis of only those tissues coming in contact with the bacteria (CEAs, ciliated ducts, and light organ epithelium) is altered by bacterial colonization of the light organ. Therefore, V. fischeri apparently makes no major metabolic contribution to E. scolopes beyond light production, and post-embryonic development of the light organ is essentially symbiont independent.
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  • 69
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    Role of the statolith in functioning of the acceleration receptor system in squids and sepioids (2000)
    Wiley
    In:  Journal of Zoology, 250 (1). pp. 31-55.
    Details
    Publication Date: 2021-06-23
    Description: Morphology of statoliths and anatomy of statocysts were studied in five species of Gonatidae, Moroteuthis robusta (Onychoteuthidae) and Galiteuthis phyllura (Cranchiidae) from the northern Bering Sea, and Todarodes pacificus (Ommastrephidae) from the Pacific waters near Japan. A special experiment was carried out in order to observe statolith mobility on the macula statica and possible endolymph flows within the statocyst in freshly caught gonatid squid Berryteuthis magister. It was found that the statolith may deviate at small acute angles around three axes running through its centre of rotation (located near the spur) without any visual damage of its attachment area to the macula. This finding enabled us to re-consider previous theories and to create a new model of the squid statocyst functioning with the statolith as detector of multidimensional movement. Two types of statolith morphology are distinguished: demersal type statoliths characteristic of near-bottom decapods, and pelagic type statoliths characteristic of all pelagic squids and not dependent on their systematic position. Phylogenetic and ecological features of the statocyst and statolith structure are established. Possible evolutionary trends in development of different types of statocysts in decapods are discussed.
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  • 70
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    Oxidative stability of lipids from squid tissues (2001)
    Wiley
    In:  Fisheries Science, 67 (4). pp. 738-743.
    Details
    Publication Date: 2021-07-02
    Description: Oxidative stability of lipids from squid tissues was compared with those of other marine lipids. On the basis of peroxide formation, total lipids (TL) from squid viscera or squid muscle with skin were most oxidatively stable, followed by squid eye TL, trout egg TL, bonito oil, and tuna orbital TL, respectively. This tendency in oxidative stabilities was also confirmed by the decrease in unoxidized polyunsaturated fatty acids during oxidation. Analyses of tocopherol contents and lipid compositions suggested that the higher oxidative stabilities of three kinds of squid tissue TL and trout egg TL compared to those of bonito oil and tuna orbital TL would be mainly because of the presence of phospholipids (PL) in squid tissue lipids and trout egg TL. However, the oxidative stability of lipids containing PL did not always decrease with increasing PL contents and stability was strongly influenced by PL composition. As squid viscera contained more than 25% of TL and these lipids were oxidatively stable, squid viscera may be used as a good resource of functional lipids rich in eicosapentaenoic acid and docosahexaenoic acid.
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  • 71
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    Remotely sensed mesoscale oceanography and the distribution of Illex argentinus in the South Atlantic : Illex argentinus and mesoscale oceanography (2001)
    Wiley
    In:  Fisheries Oceanography, 10 (2). pp. 207-216.
    Details
    Publication Date: 2021-07-05
    Description: In this study, we consider the influence of mesoscale oceanographic processes around the Falkland Islands (Islas Malvinas) in the South-west Atlantic, during the period in which the commercial squid fishery for Illex argentinus operates. Spatially referenced fishery data and satellite-derived advanced very high resolution radiometry (AVHRR) sea surface temperature (SST) data were examined using geographic information system (GIS) techniques. The distribution and relative abundance of I. argentinus in the Falkland Islands fishery was examined for the period 1989–96. Three consistent areas of high abundance were observed to the north-east (shelf-break region) and north-west (shelf region) of the islands, and close to the northern coast of East Falkland. Areas of high sea surface temperature gradients (thermal gradients) extracted from remotely sensed satellite images were used as an indicator of mesoscale oceanographic activity and compared with the location of the fishery. I. argentinus were found to be associated with areas of thermal gradients, commonly seen at the interface of Falkland Current and Patagonian shelf waters. The techniques used in this analysis allow the overlay and analysis of physical oceanographic and fishery data with potential applications in fisheries management and operational fisheries oceanography.
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  • 72
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    Monitoring a marine ecosystem using responses of upper trophic level predators: Combining ecological time-series (2001)
    Wiley
    In:  Journal of Animal Ecology, 70 (5). pp. 747-760.
    Details
    Publication Date: 2021-07-02
    Description: This study examined the changing status of the marine ecosystem at the island of South Georgia (Southern Ocean) using up to 27 variables measured over 22 years from three upper trophic level predators that specialize in foraging upon krill (Eupuasia superba Dana). These variables included population size, breeding performance, offspring growth rate, foraging behaviour and diet. A method was developed for reducing these multivariate time-series to a single vector, called a combined standardized index (CSI). 2 Sensitivity analyses showed that missing values had a large effect upon the accuracy of the CSI but this effect was reduced if the individual variables were highly correlated. The level of correlation and proportion of missing values within the empirical data set were within the acceptable range. Individual variables had widely varying influence upon the CSI but, in general, those with longer time-series had the greatest influence. 3 Principal components analysis showed that variables representing offspring growth tended to explain the greatest proportion of the variability in the CSI and this was followed by variables representing diet. 4 There were 3 years in which the CSI showed extreme and significantly low values. There was a significant non-linear functional response (similar to the Holling Type II functional response) between the overall CSI and krill biomass and a similar relationship existed when the CSI was calculated for each species individually. 5 Separate analysis of variables that were likely to be representative of changing population size showed the presence of a significant decline between 1977 and 1998. There was no trend in the CSI from variables representative of foraging conditions during the summer breeding season. The study has shown that the marine ecosystem at South Georgia shows acute but transient variability that is amplified in the response of upper trophic-level predators. There is less certainty that trends in populations are a consequence of shifts in the degree to which the ecosystem can support krill-feeding seals and penguins.
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  • 73
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    Species-specific microsatellite loci for the European squid (Loligo vulgaris) (2003)
    Wiley
    In:  Molecular Ecology Notes, 3 (2). pp. 312-313.
    Details
    Publication Date: 2021-07-12
    Description: A microsatellite dinucleotide-enriched library was obtained from the European squid (Loligo vulgaris) and five species-specific dinucleotide markers were optimized. These markers are highly polymorphic with average expected heterozygosity ranging from 0.706 to 0.927 and allele number ranging from 7 to 17. This set of primers is suitable for population genetic studies.
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  • 74
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    New microsatellite markers for assessment of paternity in the squid Loligo forbesi (Mollusca: Cephalopoda) (2000)
    Wiley
    In:  Molecular Ecology, 9 (1). pp. 110-112.
    Details
    Publication Date: 2021-07-05
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  • 75
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    Microsatellite markers for investigating population structure in Octopus vulgaris (Mollusca: Cephalopoda) (2000)
    Wiley
    In:  Molecular Ecology, 9 (5). pp. 641-642.
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    Publication Date: 2021-07-05
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  • 76
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    A review of reproductive strategies in cephalopods (2001)
    Wiley
    In:  Biological Reviews, 76 (3). pp. 291-304.
    Details
    Publication Date: 2021-07-05
    Description: Cephalopod reproductive strategies are reviewed in order to clarify their current, confusing status. Based on the type of ovulation, spawning pattern and growth between egg batches or spawning periods, five comprehensive and flexible cephalopod reproductive strategies are defined. Accordingly, with these three factors the following classification is proposed. (a) Spawning once (formerly semelparity) consisting of simultaneous terminal spawning, with synchronous ovulation, monocyclic spawning and absence of growth between egg batches. (b) Spawning more than once (formerly iteroparity) including: (i) polycyclic spawning with egg-laying occurring in separate batches during the spawning season and growth occurring between production of egg batches and spawning seasons; (ii) multiple spawning, with group-synchronous ovulation, monocyclic spawning and growth between egg batches; (iii) intermittent terminal spawning, with group-synchronous ovulation, monocyclic spawning and no growth between egg batches; (iv) continuous spawning, with asynchronous ovulation, monocyclic spawning and growth between egg batches. Examples of species exhibiting each of these reproductive strategies are given. The large amount of inter-species variation in several life-history traits related to reproductive events is discussed.
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  • 77
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    Growth of young cuttlefish, Sepia officinalis (Linnaeus 1758) at the upper end of the biological distribution temperature range (2001)
    Wiley
    In:  Aquaculture Research, 32 (11). pp. 923-930.
    Details
    Publication Date: 2021-07-02
    Description: Individual growth rates, feeding rates (%BWd−1) and food conversions for cuttlefish (S. officinalis) hatchlings and juveniles were determined during this study. A flow-through system was used. Water temperature reached 30 °C during the hottest part of the day, gradually decreasing to 25 °C during the night; salinity varied between 37 ± 3 ppt and lights were kept on for 14 h day−1. Hatchlings were placed in separate compartments with a water volume of 1.2 L. Juvenile cuttlefish (from 0.5 to 25 g) were placed in bigger baskets, with a water volume of 5.2 L. Water flow was 120 L h−1. The biggest cuttlefish used in these experiments (〉 25 g) were gathered in groups of five and placed in circular tanks (water volume of 250–300 L). Thus, results obtained in this case are means and not individual data. During the first 10, 20, 30 and 40 days, mean growth rates (of all individuals sampled by age group) decreased consistently (11.8 ± 4.1, 9.8 ± 1.8, 8.1 ± 2.2 and 7.3 ± 0.7%BW−1 respectively); in similar fashion, mean feeding rates decreased with age group (33.7 ± 13.5, 22.0 ± 7.9, 17.3 ± 3.9 and 16.7%BWd−1 respectively). Mean food conversions varied between 3.6 and 2.5 between the age groups. When grouping results by weight class, similar patterns occur, as growth and feeding rates decrease consistently as cuttlefish grow bigger. Highest mean growth and feeding rates are obtained by hatchlings (〈 0.1 g) with 12.4 ± 4.5 and 35.3 ± 15.1%BWd−1, respectively, while the lowest growth and feeding rates were recorded for the largest animals, between 15 and 25 g (3.4 ± 1.1 and 10.8 ± 4.1%BWd−1 respectively). For these weight classes, mean food conversions varied between 2.7 ± 0.9 and 3.8 ± 2.8.
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  • 78
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    The reproductive features of a mature female of the deep sea planktonic squid Galiteuthis glacialis (Cephalopoda: Cranchiidae) from the Southern Ocean (2003)
    Wiley
    In:  Polar Research, 22 (2). pp. 395-397.
    Details
    Publication Date: 2021-07-15
    Description: A mature female Galiteuthis glacialis (430 mm mantle length) was caught south of the Falkland Islands (53°S, 58°W) at a depth of 976-1001 m over a bottom depth of 1582-2378 m. A total of 8 spermatangia (15-19 mm in length) were found inserted into the mantle wall, which was of gelatinous consistency. Its ovary contained 3 605±42 oocytes, mostly 2.2-2.5 mm in length, and there were 21 ripe eggs (3.0-3.2±2.2-2.7 mm) in the oviducts. Only one resorpting oocyte (1.4 mm) was found. This is the only description of a mature female of this species, though two spent females have been previously described and three more mentioned by other authors.
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  • 79
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    A description of the nuchal organ, a possible photoreceptor, in Euprymna scolopes and other cephalopods (2000)
    Wiley | The Zoological Society of London
    In:  Journal of Zoology, 252 (2). pp. 163-177.
    Details
    Publication Date: 2021-07-20
    Description: A type of apparent photoreceptor, the nuchal organ, is described in the sepiolid squid Euprymna scolopes. These vesicles are identified in a variety of other cephalopod species. The nuchal organs have specific structural similarities to the already well-described photosensitive vesicles. Both organs have a distinct vesiculate structure and possess a rind consisting of several types of cells. Certain rind cells from both organs send processes with microvilli into the lumen of the vesicle forming a core area. Within the cores of both organs numerous microvilli occupy much of the core volume. These histological similarities provide strong evidence that the nuchal organs, like the photosensitive vesicles, are photoreceptors. Three distinct differences also exist between the nuchal organs and photosensitive vesicles: (1) the location of the nuchal organs differs from that of all known photosensitive vesicles in cephalopods; (2) the location of the nuchal organs is highly conservative in decapod cephalopods compared to the varying locations of the photosensitive vesicles; (3) the degree of structural order generally found within photosensitive vesicles is not apparent in the nuchal organs. The function of the nuchal organ is probably different from previously described photoreceptors in cephalopods.
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    A deep-sea octopus (Graneledone cf. boreopacifica) as a shell-crushing hydrothermal vent predator (2000)
    Wiley
    In:  Journal of Zoology, 252 (3). pp. 335-341.
    Details
    Publication Date: 2021-06-30
    Description: he gut contents of a female specimen of Graneledone cf. boreopacifica collected from the caldera wall of Axial Volcano, near an active hydrothermal vent in the Northeast Pacific Ocean are reported. At least 30 individual gastropods and 46 individual polychaetes are represented in the gut contents by hard parts. Shell fragments and shells removed from the gut allow ready identification of the gastropods Provanna variabilis and Lepetodrilus fucensis, both of which are known only from North Pacific hydrothermal vents. Jaws of polychaete worms are identified as those of the nereidid, Nereis piscesae, and the predatory polynoids, Levensteiniella kincaidi and an unidentified species in the subfamily Branchinotogluminae. Not only was a considerable volume of prey hard parts ingested, the gastropod shells had been crushed before being ingested. The large size of the beaks in this genus of octopus and the increased area they offer for insertion of the superior mandible muscle, the prime mover in beak closure, support the hypothesis that these beaks exert sufficient force to crush the gastropod shells. Although cephalopods had been reported to be absent from hydrothermal vents, the data presented here demonstrate that not only do they occur in vent habitats, they actively prey on vent fauna.
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  • 81
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    The importance of the Patagonian Shelf for top predator species breeding at South Georgia (2002)
    Wiley
    In:  Aquatic Conservation: Marine and Freshwater Ecosystems, 12 (1). pp. 101-118.
    Details
    Publication Date: 2021-07-05
    Description: 1. The rich zooplankton, fish and squid resources on the Patagonian Shelf sustain substantial populations of largely resident seabirds and marine mammals. These habitats are also visited seasonally by similar species from elsewhere but few data exist on their status and origin. Recent studies, using satellite-tracking to determine foraging ranges and feeding areas of seabirds and marine mammals breeding at South Georgia, have shown that several species make substantial use of the waters of the Patagonian Shelf. 2. Wandering albatrosses use shelf-edge areas year-round with direct observations of both sexes of almost all age classes, including, breeding, pre-breeding and non-breeding individuals. White-chinned petrels and female Northern and Southern giant petrels mainly visit during incubation and post-breeding, particularly to the Falklands Current (White-chinned petrels) and to upwelling areas around the southern shelf-break from the Burdwood Bank in the east to Staten Island and Diego Ramirez in the west (giant petrels). Northern giant petrel males during incubation and Antarctic fur seals in winter reach inner shelf habitats in the northern sector. In contrast, South Georgia populations of black-browed and grey-headed albatrosses do not appear to use the Patagonian Shelf at any stage of their breeding cycle. 3. Although the use of the Patagonian Shelf by visiting species is now best documented for South Georgia species, recent observational data confirm that seabirds from Diego Ramirez, Tristan da Cunha and Gough visit the southern and northern sectors, during both breeding and non-breeding seasons respectively. Several Antarctic species (notably Antarctic fulmar and cape petrel) winter in the region as do at least two albatross species from New Zealand; other species (especially Wilson's storm petrels) use it as a staging ground on migration, as do several species of baleen whales and possibly other cetacean species. 4. Three of the seabird species which breed on the Patagonian Shelf are Globally Threatened; seven of the visiting species (and four baleen whale species) also have this status. The Patagonian Shelf is, therefore, not only of global importance for the diversity and abundance of its resident top predators but is just as critical for the survival of many visiting species, some of which are even more endangered. 5. Combining data from satellite-tracking with conventional mapping from direct observations offers the prospect of defining the foraging ranges (and the main feeding areas within these) of a range of key top predator species. Such data should be used, in conjunction with similar information of the distributions of fish, squid and zooplankton resources and of fishing effort, to identify critical marine habitats whose precautionary, multiple-use sustainable management will be vital to protect the interests of both commercial fishers and top predators.
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  • 82
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    Crustal structure of the central Sunda margin at the onset of oblique subduction (2001)
    Wiley
    In:  Geophysical Journal International, 147 (2). pp. 449-474.
    Details
    Publication Date: 2018-07-16
    Description: The convergent margin of the central Sunda Arc in Indonesia was the target of a reflection and refraction seismic survey conducted in 1998 and 1999. Along two seismic lines across the subduction complex off southern Sumatra and off Sunda Strait, coincident multichannel and wide-angle data were collected, complemented by two refraction strike-lines in the forearc basin off Sumatra. The combined analysis of the acquired data allows us to present a detailed model of the subduction zone where initiation of strain partitioning occurs due to the onset of oblique subduction. The dip of the subducted plate is well defined along both dip-lines and a lateral increase from 5° to 7° from beneath the outer high off Sumatra to Sunda Strait is supported by complementary gravity modelling. The downgoing slab is traced to a depth of more than 30km. On both reflection dip-lines, a clearly developed backstop structure underlying a trench slope break defines the landward termination of the active accretionary prism and separates it from the outer high. Active subduction accretion is supported by laterally increasing velocities between the deformation front and the active backstop structure. Seismic velocities of the outer high are moderate along both lines (〈5.8kms−1 at 20km depth), suggesting a sedimentary composition. Reduced reflectivity beneath a rugged top basement traced along the outer high of both dip-lines supports a high degree of deformation and material compaction. Several kilometres of sediment has accumulated in the forearc domain, although a distinct morphological basin is only recognized off southern Sumatra and is not developed off Sunda Strait. The bathymetric elevation of the Java shelf that is encountered in the southern Sunda Strait corresponds to increased velocities of a basement high there and is connected to extensional structures of the Sunda Strait transtensional basin. Differences observed in the morphology of the forearc domain are also reflected in the lower crustal structure. Off southern Sumatra, the velocity–depth model clearly indicates a continental-type crust underlying the forearc basin, whereas lower velocities are found beneath the Sunda Strait forearc domain. Off Sumatra, some 3-D constraint on the upper plate structure is gained from the refraction strike-lines, which in addition is supported by synthetic data modelling.
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  • 83
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    Multiple mantle sources during island arc magmatism: U-Pb and Hf isotopic evidence from the Kohistan arc complex, Pakistan (2002)
    Wiley
    In:  Terra Nova, 14 . pp. 461-468.
    Details
    Publication Date: 2018-01-22
    Description: This paper presents high-precision U–Pb ages and initial Hf isotopic compositions of zircon from mafic to felsic rocks of the Kohistan Arc Complex, Pakistan. Three magmatic pulses tapping geochemically different reservoirs are distinguished. Partial melting of mantle with MORB-type isotopic characteristics generated 99–92-Ma-old magmas. Plutonism around 85 Ma tapped a more fertile mantle source, most likely consisting of a 〉600-Ma-old metasomatically enriched mantle, or of mantle contaminated by an old sedimentary component; 82-Ma-old felsic peraluminous dykes have MORB-type isotopic compositions considered to be inherited from remelting earlier magmas in the deep base of the arc. The isotopic results demonstrate several and rather rapid changes in melt source region during arc development. They also show that there was subordinate continental influence and negligible importance of slab components for the Hf budget during the generation of the Kohistan Arc Complex.
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  • 84
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    En-route investigations of plankton in ballast water on a ship's voyage from the Baltic to the open Atlantic coast of Europe (2000)
    Wiley
    In:  International Review of Hydrobiology, 85 (5-6). pp. 577-596.
    Details
    Publication Date: 2017-05-30
    Description: Ballast water of ships has been recognized as a major vector for the unintentional transfer of exotic aquatic organisms between and within many parts of the world. Studies in several European ports have shown that most of the ballast water discharged originates from nearby sea areas indicating the importance of secondary introductions. However, the patterns of interregional transfer of exotic species within Europe remain largely unknown. The present study examined the transfer of phyto- and zooplankton organisms in the ballast water to assess the potential for the transport of invasive aquatic species between the Baltic Sea and the open Atlantic coast of Europe. Six potentially toxic phytoplankton species were found in the ballast water examined. In four ballast water sampling trials no significant changes in abundance of both phyto- and zooplankton organisms were observed during first 3–4 days of experiment. Even in the end of the longest sampling trial (15 days) millions of plankton organisms were found. The results obtained indicate the importance of interregional European shipping in the dispersal of exotic plankton organisms.
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  • 85
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    Alkaline phosphatase activities among populations of the colony-forming Diazotrophic Cyanobacterium Trichodesmium Spp. (Cyanobacteria) in the Red Sea (2001)
    Wiley
    In:  Journal of Phycology (37). pp. 310-317.
    Details
    Publication Date: 2018-06-25
    Description: Alkaline phosphatase activities of the diazotrophic marine cyanobacterium Trichodesmium were studied among natural populations in the northern Red Sea and in laboratory cultures of Trichodesmium sp. strain WH9601. Open‐water tuft‐shaped colonies of Trichodesmium showed high alkaline phosphatase activities with 2.4–11.7 μmol p‐nitrophenylphosphate (PNPP) hydrolyzed·μg chl a−1·h−1, irrespective of date or origin of the sample. Coastal populations of the Trichodesmium tuft colonies had low alkaline phosphatase activities with 0.2–0.5 μmol PNPP·μg chl a−1·h−1. An exception was the Trichodesmium fall maximum, when both tuft colonies and the plankton community (〈100 μm) had alkaline phosphatase activities of 0.6–7.4 μmol PNPP·μg chl a−1·h−1. Likewise, the more rare puff and bow‐tie colonies of Trichodesmium spp. in coastal waters had elevated alkaline phosphatase activities (0.8–1.6 μmol PNPP·μg chl a−1·h−1) as compared with tuft colonies coinhabiting the same waters. Intact filaments of tuft‐forming Trichodesmium sp. strain WH9601 from phosphate‐replete cultures had a base alkaline phosphatase activity of 0.5 μmol PNPP·μg chl a−1·h−1. This activity underwent a 10‐fold increase in phosphate‐deplete cultures and in cultures supplied with glycerophosphate as the sole P source. The elevated level of alkaline phosphatase activity was sustained in P‐deplete cultures, but it declined in cultures with glycerophosphate. The decline is suggested to result from feedback repression of alkaline phosphatase synthesis by the phosphate generated in the glycerophosphate hydrolysis. The enhanced alkaline phosphatase activities of Trichodesmium spp. populations provide evidence that P stress is an important factor in the ecology of Trichodesmium in the northern Red Sea.
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  • 86
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    Proposal for International Agreement on Ca Notation resulting from discussion at workshops on stable isotope measurement held in Davos (Goldschmidt 2002) and Nice (EGS-AGU-EUG 2003) (2004)
    International Association of Geoanalysts | Wiley
    In:  Geostandards and Geoanalytical Research, 28 (1). pp. 149-151.
    Details
    Publication Date: 2019-08-08
    Description: A proposal is made to standardise the reporting of Ca isotope data to the δ44Ca/40Ca notation (or δ44Ca/42Ca) and to adopt NIST SRM 915a as the reference standard.
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  • 87
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    Dependency of larval fish survival on retention/dispersion in food limited environments: The Baltic Sea as a case study (2003)
    Wiley
    In:  Fisheries Oceanography, 12 . pp. 425-433.
    Details
    Publication Date: 2019-09-23
    Description: A three-dimensional hydrodynamic model has been used to analyse temporally and spatially resolved circulation patterns in the Baltic Sea with special emphasis on drifting particles representing larval fish. The main purpose of this study was (i) to investigate potential drift patterns of larval fish, (ii) to identify its intra- and inter-annual variability for time periods based on the timing of spawning and (iii) to analyse its seasonal and spatial variability in dependence of the atmospheric forcing conditions. For the time period 1979–1998 temporally and spatially resolved simulated flow fields were used to describe the potential drift from the centre of main reproductive effort of Baltic cod (Gadus morhua). The results of the model runs demonstrate a general change in circulation pattern from retention during a first decade (1979–1988) to dispersion in the following decade (1989–1998). This increase in dispersion was related to an increase in the variability of the local wind forcing conditions over the Baltic. The more frequent occurrence of dispersion in spring of the recent decade was accompanied by a strong decay in biomass of one of the main larval fish feeding component in the central basin, the calanoid copepod Pseudocalanus elongatus. Larger dispersion of this prey organism may have affected the spatial overlap and thus the contact rates between predator and prey. Hence, this may have resulted in a food limitation for early life stages of Baltic cod and potentially contributed to the pronounced shift in cod peak spawning time from spring to late summer. Early life stages of cod originating from late spawning fish, benefited from a stronger dispersion in late summer and autumn, into shallow coastal areas with higher calanoid abundance.
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  • 88
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    Traveltime approximation for a reflected wave in a homogeneous anisotropic elastic layer (2002)
    Wiley
    In:  Geophysical Journal International, 151 (1). pp. 172-183.
    Details
    Publication Date: 2018-07-17
    Description: An approximation to the traveltime field is calculated for an elastic wave that propagates in a homogeneous anisotropic layer and is reflected at a plane boundary. The traveltime is approximated by a Taylor series expansion with the third derivative of the traveltime being taken into account. The coefficients of the series refer to the seismic ray, which is locally the fastest ray. Simple formulae are obtained for orthorhombic media in the crystal coordinate system, which relate the traveltimes of the reflected waves to the elastic constants of the medium. A numerical example is presented for wave propagation in orthorhombic olivine, which is a constituent of the Earth's mantle. A second example is given by an isotropic host rock with a set of parallel cracks, which is an important model for wave propagation in the Earth's crust. The elastic parameters can be determined by measuring the reflection times as a function of source–receiver offset. The approximate traveltime–distance curves are compared with traveltimes obtained from seismic ray tracing.
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  • 89
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    Complementary impact of copepods and cladocerans on phytoplankton (2001)
    Wiley
    In:  Ecology Letters, 4 (6). pp. 545-550.
    Details
    Publication Date: 2017-02-22
    Description: The differences in the impact of two major groups of herbivorous zooplankton (Cladocera and Copepoda) on summer phytoplankton in a mesotrophic lake were studied. Field experiments were performed in which phytoplankton were exposed to different densities of two major types of herbivorous zooplankton, cladocerans and copepods. Contrary to expectation, neither of the two zooplankton groups significantly reduced phytoplankton biomass. However, there were strong and contrasting impacts on phytoplankton size structure and on individual taxa. Cladocerans suppressed small phytoplankton, while copepods suppressed large phytoplankton. The unaffected size classes compensated for the loss of those affected by enhanced growth. After contamination of the copepod mesocosms with the cladoceran Daphnia, the combined impact of both zooplankton groups caused a decline in total phytoplankton biomass.
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  • 90
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    Big Effects from Small Changes: Possible Ways to Explore Nature's Chemical Diversity (2002)
    Wiley
    In:  ChemBioChem, 3 (7). pp. 619-627.
    Details
    Publication Date: 2016-02-23
    Description: Fungi or bacteria that produce secondary metabolites often have the potential to bring up various compounds from a single strain. The molecular basis for this well-known observation was confirmed in the last few years by several sequencing projects of different microorganisms. Besides well-known examples about induction of a selected biosynthesis (for example, by high- or low-phosphate cultivation media), no overview about the potential in this field for finding natural products was given. We have investigated the systematic alteration of easily accessible cultivation parameters (for example, media composition, aeration, culture vessel, addition of enzyme inhibitors) in order to increase the number of secondary metabolites available from one microbial source. We termed this way of revealing nature's chemical diversity the 'OSMAC (One Strain–Many Compounds) approach' and by using it we were able to isolate up to 20 different metabolites in yields up to 2.6 g L−1from a single organism. These compounds cover nearly all major natural product families, and in some cases the high production titer opens new possibilities for semisynthetic methods to enhance even more the chemical diversity of selected compounds. The OSMAC approach offers a good alternative to industrial high-throughput screening that focuses on the active principle in a distinct bioassay. In consequence, the detection of additional compounds that might be of interest as lead structures in further bioassays is impossible and clearly demonstrates the deficiency of the industrial procedure. Furthermore, our approach seems to be a useful tool to detect those metabolites that are postulated to be the final products of an amazing number of typical secondary metabolite gene clusters identified in several microorganisms. If one assumes a (more or less) defined reservoir of genetic possibilities for several biosynthetic pathways in one strain that is used for a highly flexible production of secondary metabolites depending on the environment, the OSMAC approach might give more insight into the role of secondary metabolism in the microbial community or during the evolution of life itself.
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  • 91
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    Effects of very low calcium intake on calcium metabolism in pubertal girls (2001)
    (FASEB) Federation of American Societies for Experimental Biology | Wiley
    In:  FASEB Journal, 15 (5). A1095-A1095.
    Details
    Publication Date: 2022-01-13
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  • 92
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    Public-driven responses to global environmental change (2002)
    Wiley
    In:  Responding to global environmental change | Encyclopedia of global environmental change
    Details
    Publication Date: 2022-03-21
    Type: info:eu-repo/semantics/bookPart
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  • 93
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    National self-interest: A major factor in international environmental policy formulation (2002)
    Wiley
    In:  Responding to global environmental change. Encyclopedia of global environmental change
    Details
    Publication Date: 2022-03-21
    Type: info:eu-repo/semantics/bookPart
    Format: application/pdf
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